Solution for Site Multihoming in a Real IP Environment
draft-shyam-site-multi-38
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Expired".
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|---|---|---|---|
| Author | Shyam Bandyopadhyay | ||
| Last updated | 2016-11-25 | ||
| RFC stream | (None) | ||
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| Consensus boilerplate | Unknown | ||
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draft-shyam-site-multi-38
INTERNET DRAFT S. Bandyopadhyay
draft-shyam-site-multi-38.txt November 26, 2016
Intended status: Experimental
Expires: May 26, 2017
Solution for Site Multihoming in a Real IP Environment
draft-shyam-site-multi-38.txt
Abstract
This document provides a solution for Site Multihoming of stub
networks in a real IP environment. Each user interface in a customer
network may have as many global unicast addresses as many service
providers it will be connected with. Users can establish multiple
connections through different service providers simultaneously.
Customer networks can maintain private address space to communicate
within its users. Customer networks can provide IP mobility services
as well.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 26, 2017.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
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Table of Contents
1. Introduction.....................................................2
2. Solution for site multihoming....................................3
2.1. Selection of source and destination address ...................5
2.1.1. Path selection...............................................6
2.1.2. Link failure and switch over to an alternate route...........7
2.2. Multihoming and IP Mobility...................................12
2.2.1. IP Address Stacking.........................................13
2.3. Implementation aspects........................................17
2.3.1. Processing of system call 'getsrcaddr'......................18
2.3.2. Processing of 'gethostbynamewithsrcaddr'....................19
2.3.3. Changes required in ip_output and ip_forwarding modules.....21
2.3.4. Processing of protocol input routines and socket IO
system calls................................................22
2.4. Multihoming and VPN...........................................22
3. Security Consideration..........................................23
4. IANA Consideration..............................................23
5. Normative References............................................23
6. Informative References..........................................24
7. Author's Address................................................24
1. Introduction
Based on the definition of "multihoming" as stated in RFC3582[1],
"A "multihomed" site is one with more than one transit provider.
"Site-multihoming" is the practice of arranging a site to be
multihomed."
This is a general solution for site multihoming of stub networks in a
real IP world irrespective of the framework supported by the service
provider network. The solution is applicable to any customer network
that receives globally unique IP addresses for all of its nodes and
communicates with the rest of the world without the help of NAT[15].
It is applicable to any version of IP, i.e. IPv4, IPv6 or any new
generation of IP that may emerge by removing the drawbacks associated
with IPv6[7]. Within a provider assigned address space, each customer
network will possess as many global unicast address space as many
service providers it gets connected with. So, an user interface of a
host may have as many global unicast addresses as many service
providers it will be connected with.
Users can maintain multiple connections through multiple service
providers simultaneously. A customer network can maintain private IP
addresses to communicate within its users. Communication using
private IP is restricted to private IP space for the sake of privacy.
Customer networks can provide IP mobility support as well.
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There are many variants of UNIX systems (as well as real time
operating systems) which make use of BSD source code for their
implementation of TCP/IP stack. The solution given below highlights
the changes required with the BSD release 4.4 source code with the
notations used by IPv4. It addresses issues relevant to IPv6 wherever
applicable. All other implementations of TCP/IP have to be updated
in the similar manner.
In this document the term "default router" will refer to the customer
edge (CE) router that communicates with the provider network. Also
the term "intermediate routers" will refer to all the routers apart
from the CE routers.
2. Solution for site multihoming
RFC1122[2] made an extensive study related to different aspects of
multihoming. Some of the requirements suggested in that document
related to UDP and the application layer were avoided for multihomed
hosts in a connected network with a single gateway to reach the
outside world. This was achieved by the implementation of TCP/IP by
making sure that the interface address of an outgoing packet gets
selected based on the route to be followed by the destination
address. This criterion holds good in a connected environment with a
single gateway to reach the outside world. Once more than one gateway
comes into play to reach the outside world, either routing table of
the entire world has to be brought in or needs some enhancements
within the existing system to make the things work.
Whenever a customer network gets service from more than one service
provider, the customer network can be viewed as having multiple
source-id (user-id) space. Each of these IP domain gets connected to
different service providers through different routers. So each
interface of customer network may have as many global unicast
addresses as many service providers it is connected with. Number of
routing entries in the routing table will (roughly) become a multiple
of IP domains that it supports. Communication between any two hosts
within the customer network will follow the traditional routing
mechanism. In order to provide multihoming services it is needed that
a host computer always forwards packets to the customer edge router
associated to the same IP domain while communicating to someone in
the outside world. i.e. if the interface of a host computer H
receives an IP address 'addr1' and 'addr2' from two service providers
P1 and P2 which are connected through routers R1 and R2 respectively,
host H has to forward a packet to R1 while using its IP address as
'addr1' in order to send packets to the outside world. So, host
computers as well as the intermediate routers have to use default
routing based on the source domain of the source address in the IP
header.
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In order to achieve this, host computers as well as intermediate
routers need to have information related to its IP domain (net
address/net mask) and the associated default router for all of its IP
domains. They need to have a route entry per IP domain for all of its
default routers. These information should be uploaded at the system
start up time.
Routing of IP packets (in the ip_output module of the hosts and in
the ip_forwarding module of the intermediate routers) need to be
modified in the following manner.
If destination address of a packet falls outside of its IP domains,
it has to be forwarded to the default router based on the domain that
the source address belongs to.
If destination address of the IP header falls within any one of its
IP domains, usual routing mechanism has to be followed.
If customer network maintains private IP domain, communication using
private IP has to be restricted within private IP space.
UDP (or RAW) based servers that need to support multiple clients
simultaneously need to respond to a client's request with the same
source address that the client had specified as the destination
address. In order to satisfy this, system needs to introduce two
system calls along with the existing system calls (i.e. read, write,
send, sendto, recv, recvfrom)
ssize_t recvwithdstaddr (int sockfd, char *buf, size_t nbytes,
int flags, struct sockaddr *from, socklen_t *fromlen,
struct sockaddr *fromcladdr, socklen_t *fromcladdrlen,
struct sockaddr *dst, socklen_t *dstlen,
struct sockaddr *dstcladdr, socklen_t *dstcladdrlen);
'recvwithdstaddr' receives data with destination address as specified
by the sender. It is similar to 'recvfrom' with the additional field
'dst' related to the address of the receiving interface of the host.
'fromcladdr' and 'dstcladdr' will hold the values of co-located care-
of addresses (see section 2.2) of source and destination if they
happen to be mobile.
ssize_t sendwithsrcaddr (int sockfd, char *buf, size_t nbytes,
int flags, struct sockaddr *to, socklen_t tolen,
struct sockaddr *dstcladdr, socklen_t dstcladdrlen,
struct sockaddr *src, socklen_t srclen,
struct sockaddr *srccladdr, socklen_t srccladdrlen);
'sendwithsrcaddr' sends data specifying the source address of the
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outgoing interface of the host. It is similar to 'sendto' with
additional parameters related to source address. It behaves like
'sendto' if no address is specified for 'src'. 'srccladdr' and
'dstcladdr' will hold the values of co-located care-of addresses of
source and destination.
All the UDP based servers that need to support multiple clients
simultaneously, need to replace 'sendto' with 'sendwithsrcaddr' and
'recvfrom' with 'recvwithdstaddr'.
It has been expressed in several documents including RFC4291[3], that
a single interface will possess multiple IP addresses in a real IP
environment. In these cases, all the UDP servers have to be updated
with the system calls 'sendwithsrcaddr' and 'recvwithdstaddr' even if
a customer site gets attached to a single gateway to reach the
outside world.
The same logic will apply to server applications with RAW sockets.
Server applications that are TCP based should work in the usual
manner.
2.1. Selection of source and destination address
If a source network is connected with 'n' service providers and the
destination network is connected with 'm' service providers, there
will be a possible 'm*n' combination of source-destination pairs for
connection between source and destination. So, application program
needs to select a source and destination address before initiating
communication with the destination.
A system call needs to be introduced to get the source address based
on the destination address. If application program needs to use the
destination address directly, it needs to use this system call.
int getsrcaddr(int sockfd, struct in_addr *dst, struct in_addr *src);
It returns the number of source addresses that can be used. The
addresses will be available from 'src', which is an array of type
struct in_addr. The 'src' addresses will be available in sorted
manner. Application program needs to use these source addresses from
the top (i.e. the 0th) to establish connection with the destination.
'sockfd' is used to get the 'type of service' assigned. So, an
application program needs to set its type of service before using
this call.
Client applications need to use 'getsrcaddr' and 'bind' the source
address before communicating with their peer.
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Users may use name instead of IP address to reach the destination.
The usual procedure is to use the system call 'gethostbyname' to
resolve the destination address and then to use the same for
communication. The destination may also be multihomed. In order to
find out the best possible choice to reach the destination, another
system call needs to be introduced.
struct hostent *gethostbynamewithsrcaddr(int sockfd, const char *name,
int *ndst, struct addr_pair *dst);
where 'addr_pair' is defined as
struct addr_pair {
struct in_addr src;
struct in_addr dst;
};
'gethostbynamewithsrcaddr' takes 'name' and 'sockfd' as input
parameters and finds out the best possible route to reach the
destination. It returns the pointer to the 'hostent' structure as
returned by 'gethostbyname' system call. The parameter 'ndst' gets
the number of possible routes to be used and the corresponding source
and destination addresses gets assigned to 'dst' in sorted manner.
'sockfd' is used to get the 'type of service' assigned. So, an
application program needs to set its type of service before using
this call.
2.1.1. Path selection
Paths are selected by sending RSVP messages from user to the PE
routers using MPLS UNI[12] with the following changes in respective
modules.
In order to transport a packet from one network to another, provider
network sets up a LSP. In RSVP[10,11], resource reservation is
receiver-initiated. In the Path message, the sending application
construct Path message using RSVP SENDER_TSPEC and ADSPEC objects.
The path properties of ADSPEC object gets modified by the network
elements as the Path message moves from sender to receiver. The
receiver makes use of SENDER_TSPEC and ADSPEC objects and forms
FLOWSPEC object and sends back to the network element towards the
sender. In order to make decision which path an application should
select from multiple possible paths due to multihoming, ADSPEC object
that was received by the receiver has to be passed back to the sender
by appending them with the Resv message.
For best effort service, path is selected based on widest-shortest
path approach, i.e. the path having the maximum effective available
bandwidth with minimum NUMBER_OF_IS_HOPS. Effective available
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bandwidth is calculated as
bandwidth allocated to the customer
----------------------------------------- * AVAILABLE_PATH_BANDWIDTH
gross effective bandwidth allocated to customers
If (Effective available bandwidth > unused bandwidth
allocated to the customer)
Effective available bandwidth = unused bandwidth
allocated to the customer.
When a Path message is sent from a user to the ingress PE router, for
best-effort service the PE router sets up a LSP with the egress PE
router and stores the path attributes with the ADSPEC objects if no
LSP has already been created. The ingress PE router sends the path
attributes (with AVAILABLE_PATH_BANDWIDTH set as Effective available
bandwidth) to the sender. If ingress PE router finds an existing LSP
for the destination node, it sends the path attributes associated to
the LSP.
PE routers need to maintain a list of customers that have accessed
the LSP with the last time of access. At the end of each RSVP refresh
time, it needs to check the list and delete those entries whose last
time of access exceeds the time period of RSVP refresh time. Gross
effective bandwidth is calculated as the sum of bandwidths allocated
to all the customers available in the list.
The above equation is applicable when communication takes place
between global unicast/multicast addresses. In case of VPN, service
providers allocate fixed bandwidth path between two customer
locations. So, when communication takes place between private
addresses actual unused bandwidth of that path has to be returned.
For Guaranteed bandwidth[14] and Controlled-Load service[13] path is
selected with MINIMUM_PATH_LATENCY with minimum NUMBER_OF_IS_HOPS,
also sender applications need to send PathTear messages for all the
paths that are not selected.
A PE router will be in a different address space than the address
space of the customer network. As hosts need not be aware of the PE
routers, hosts need to send queries to the CE router to get the
address of the PE router and store the same in their cache, the way
it works with DNS.
2.1.2. Link failure and switch over to an alternate route
As stated in section 2.1, there are possible "m*n" routes. Client
applications select any one of them for communication. If
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communication fails due to link failure, it may be desirable to
switch over to an alternate route (application programs must ensure
that it conforms to the requirement of the application).
In reality link failure is a rare phenomenon; so detection of link
failure should not become an overhead for the network. Fault gets
detected first at the local site where the fault is associated with.
Say, if CE-PE link fails, it is the CE router that comes to know
about it at the beginning. So, the local site needs to take
initiative for the switchover operation. When failure happens,
system generates trap which triggers the operation for switchover to
an alternate route.
The steps can be summarized as follows:
o When client application calls 'getsrcaddr' or
'gethostbynamewithsrcaddr' system finds out a list of possible
"source-destination" pairs for communication. If number of routes
happen to be more than one rest of the steps are followed.
o Client application establishes a TLS [5] session with its peer
after 5 unit tuple gets established. After handshake operation,
client application sends the list of source-destination pair to its
peer in secured mode. Exchange of routes is required because failure
may happen in the remote site too;
o Both client application and its peer store security parameters of
TLS session and the list of source-destination routes with the
protocol control block (PCB) using 'setsockopt' which informs the
system to activate switchover operation if there is a link failure;
o When CE router detects failure of CE-PE link, it broadcasts an ICMP
message ICMP_LINKFAILURE_CE_PE_LINK to all the hosts.
o On receiving ICMP_LINKFAILURE_CE_PE_LINK, system goes through the
list of PCB and gets the list of applications for which it needs to
start the switchover operation. For any such particular application,
it prepares the list of possible routes for communication through the
active links. It tries to set alternate route to its peer by sending
ICMP message ICMP_LINKFAILURE_SET_ALT_ROUTE in secured mode with the
best possible route.
o On receiving ICMP_LINKFAILURE_SET_ALT_ROUTE, peer host checks
whether there is any application in the list of PCB where the request
will be applicable. On finding the right PCB, it sets the alternate
route and sends a message ICMP_LINKFAILURE_ALT_ROUTE_ESTABLISHED to
its peer.
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o On receiving ICMP_LINKFAILURE_ALT_ROUTE_ESTABLISHED, system sets
the alternate route and completes the operation of switchover.
So, it introduces an ICMP message of type ICMP_LINKFAILURE (type 41)
with the following codes:
ICMP_LINKFAILURE_CE_PE_LINK 1
ICMP_LINKFAILURE_CE_FAILURE 2
ICMP_LINKFAILURE_SET_ALT_ROUTE 3
ICMP_LINKFAILURE_ALT_ROUTE_ESTABLISHED 4
In order to provide secured communication it needs to depend on
security protocol SSL/TLS. Security parameters e.g. secret key,
compression method and cipher spec are stored in the PCB. ICMP
messages will have two parts; information in the first part, i.e.
'struct icmp' will hold all the necessary information to locate the
connection entry in the list of PCB. The second part will hold the
information related to the operation and will be in encrypted form
with record header. So, changes within a PCB entry is allowed only
if ICMP message is received in a secured mode.
It introduces an element 'struct id_pcb' inside union 'icmp_dun' of
'struct icmp' as follows:
struct icmp {
u_char icmp_type; /* type of message, see below */
u_char icmp_code; /* type sub code */
u_short icmp_cksum; /* ones complement cksum of struct */
union {
u_char ih_pptr; /* ICMP_PARAMPROB */
struct in_addr ih_gwaddr; /* ICMP_REDIRECT */
struct ih_idseq {
uint16_t icd_id; /* network format */
uint16_t icd_seq; /* network format */
} ih_idseq;
int ih_void;
/* ICMP_UNREACH_NEEDFRAG -- Path MTU Discovery (RFC1191) */
struct ih_pmtu {
uint16_t ipm_void; /* network format */
uint16_t ipm_nextmtu; /* network format */
} ih_pmtu;
struct ih_rtradv {
u_char irt_num_addrs;
u_char irt_wpa;
u_int16_t irt_lifetime;
} ih_rtradv;
} icmp_hun;
union {
struct id_ts { /* ICMP Timestamp */
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uint32_t its_otime; /* Originate */
uint32_t its_rtime; /* Receive */
uint32_t its_ttime; /* Transmit */
} id_ts;
struct id_ip {
struct ip idi_ip;
/* options and then 64 bits of data */
} id_ip;
struct id_pcb {
u_char ipcb_ip_proto; /* protocol TCP/UDP */
struct in_addr ipcb_laddr, /* source address */
ipcb_faddr; /* destination address */
u_short ipcb_lport, /* source port */
ipcb_fport; /* destination port */
} id_pcb;
struct icmp_ra_addr id_radv;
u_int32_t id_mask;
char id_data[1];
} icmp_dun;
};
'struct inpcb' of protocol control block includes four new fields
'inp_lf_n_routes', 'inp_lf_stat', 'inp_lf_routes' and
'inp_seq_params' of type SecParams (SecParams is a type of struct
whose elements are elements of SecurityParameters as defined in
section 6.1 of RFC5246 [5]) as follows:
struct inpcb {
struct inpcb *inp_next, *inp_prev; /* doubly linked list */
struct inpcb *inp_head; /* pointer back to chain of inpcb's for
this protocol */
struct in_addr inp_faddr; /* foreign IP address */
u_short inp_fport; /* foreign port# */
struct in_addr inp_laddr; /* local IP address */
u_short inp_lport; /* local port# */
struct socket *inp_socket;/* back pointer to socket */
caddr_t inp_ppcb; /* pointer to per-protocol pcb */
struct route inp_route /* placeholder for routing entry */
int inp_flags; /* generic IP/datagram flags */
struct ip inp_ip; /* header prototype; should have more */
struct mbuf *inp_options; /* IP options */
struct ip_moptions *inp_moptions; /* IP multicast options */
u_char inp_lf_n_routes; /* number of possible routes */
u_char inp_lf_stat; /* state of switchover;
STAT_DO_NOT_ALTER(0)/STAT_ALTER(1) */
struct addr_pair *inp_lf_routes;/*pointer to the array of routes*/
SecParams inp_seq_params; /* security parameters */
};
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From application layer, the field 'inp_seq_params' is set with the
system call 'setsockopt' by introducing a new socket option
SO_SEQPARAM of level SOL_SOCKET; route information i.e.
inp_lf_n_route, inp_lf_routes and inp_lf_stat are set by system call
'setsockopt' by introducing another socket option SO_LFROUTES of
level SOL_SOCKET.
setcockopt (sockfd, SOL_SOCKET, SO_SEQPARAM, (char *)&seq_param,
sizeof(SecurityParameters));
setsockopt (sockfd, SOL_SOCKET, SO_LFROUTES, (char *)routes, sizeof
(struct addr_pair)*n_routes);
ICMP messages with 'icmp_code' ICMP_LINKFAILURE_SET_ALT_ROUTE and
ICMP_LINKFAILURE_ATL_ROUTE_ESTABLISHED will have same format as
follows:
Information of the current active link of the PCB entry i.e. protocol
id, source address, destination address, source port and destination
port are set with the fields of 'struct id_pcb' of 'struct icmp'. The
encrypted part of the message will have three fields, source address
and destination address of the alternate route and ICMP code (i.e.
ICMP_LINKFAILURE_SET_ALT_ROUTE/
ICMP_LINKFAILURE_ALT_ROUTES_ESTABLISHED) as it was set with the ICMP
header.
Recipient of these messages needs to search PCB entry in the
following manner:
If 'source port', 'destination port' and 'protocol id' of incoming
ICMP message matches with any entry in the list of PCB and the fields
'source address' and 'destination address' of the ICMP message
matches with any entry of 'inp_lf_routes' of the corresponding entry
in the PCB, it will be considered as a match. If no matching entry is
found, message has to be dropped. With the security information of
the PCB entry, the encrypted part of the ICMP message gets decrypted.
If it fails to decrypt the message or the message received with
invalid MAC, message needs to be dropped. If ICMP code in the header
does not match with that of the encrypted part, the message also
needs to be dropped.
Details of the ICMP operations are described below:
ICMP_LINKFAILURE_CE_PE_LINK
CE router detects link failure and sends this message to all the
users in the network; The field 'icmp_gwadd' of 'struct icmp' holds
the IP address of the PE router.
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ICMP_LINKFAILURE_CE_FAILURE
CE router itself may fail. It gets detected by alternate CE router.
CE routers send keep-alive messages between themselves at regular
interval to detect this failure. The field 'icmp_gwadd' of 'struct
icmp' holds the IP address of the faulty CE router.
ICMP_LINKFAILURE_SET_ALT_ROUTE
This message is sent by a host after receiving ICMP broadcast message
ICMP_LINKFAILURE_CE_PE_LINK or ICMP_LINKFAILURE_CE_FAILURE from a CE
router for all the entries of PCB whose ('inp_lf_stat' = STAT_ALTER
and source-destination route passes through the failed link), to
their peer. It maintains a list of information where each entry will
have the connection details including the best possible route. For
best effort traffic route is selected by sending echo messages and
calculating round trip delay; for the rest it follows the approach
stated in section 2.1.1. For each entry in the list, host sends
ICMP_LINKFAILURE_SET_ALT_ROUTE for (arbitrary) 'n' number of times
with an (arbitrary) interval of 't' msecs (sufficient enough for the
reply of ICMP_LINKFAILURE_SET_ALT_ROUTE comes back and gets
processed; roughly twice the round trip delay) till it receives a
positive acknowledgment ICMP_LINKFAILURE_ATL_ROUTE_ESTABLISHED from
its peer. On receiving a positive acknowledgment
ICMP_LINKFAILURE_ATL_ROUTE_ESTABLISHED, it deletes the corresponding
entry from the list and updates the route information in the PCB.
ICMP_LINKFAILURE_ATL_ROUTE_ESTABLISHED
On receiving ICMP_LINKFAILURE_SET_ALT_ROUTE, host needs to look for a
match in the PCB. If there is a match, host sends
ICMP_LINKFAILURE_ATL_ROUTE_ESTABLISHED to its peer on successful
completion of changing 'source address' and 'destination address'
with the desired value of the alternate route in the PCB. The message
will contain all the fields as that of the receiving message by
setting 'icmp_code' as ICMP_LINKFAILURE_ATL_ROUTE_ESTABLISHED both at
the header part as well as at the encrypted part.
Switchover operation requires some amount of time. This duration is
under the tolerance limit for best effort traffic. For Guaranteed
bandwidth and Controlled-Load service as the circuit needs to be
reestablished, it may cause flicker. This situation can be avoided
by maintaining back-up circuit through an alternate route. As link
failure is a rare phenomenon, this feature can be provided on on-
demand basis or based on the application type.
2.2. Multihoming, IP Mobility and Provider Independent addressing
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For a mobile node, its co-located care-of IP address[4] has to be
bound to one of the IP addresses supported by the service providers
(if mobile node advertises more than one address, the home agent will
get confused, also there are other implications). Transport layer
must ensure that the 'home address' gets tightly coupled with that
particular IP address.
A mobile node in a foreign site will have all the IP addresses
supported by the foreign site as well as its "Home Address". As the
mobile node will also communicate with the outside world with its
"Home Address", user should get a provision to choose its "Home
Address" while initiating communication. If mobile node makes use of
the address of foreign site for applications that do not need its
"Home Address" (say, accessing a web site) cost of communication will
get reduced. This feature is useful when a mobile user is in a
foreign site but remains within the same sphere of influence (say an
user lives in one city but works in a different city which is in a
different sphere of influence and likes to access web during his
working hours).
If "Home Address" is selected for communication, the transport layer
of the mobile node should use its care-of address as the source
address and pass its "Home Address" as an option field in the stack.
This is because multihoming expects the source address as the
deciding factor for packet forwarding.
The IP address of a node with a provider independent address have to
be mapped with one of the global unicast addresses. So for the
purpose of multihoming whatever will be applicable to a mobile node
will also be applicable to a node with provider independent address.
All the issues that need to be handled for IP mobility, provider
independent addressing related to multihoming have been thoroughly
discussed in section 4 of the architectural specification[7]. Please
go through that section first before going through the rest.
2.2.1. IP Address Stacking
IP address stacking in IPv6 is performed with the approach introduced
in section 6.4 of RFC6275[8] with slight modification. RFC6275
describes how to pass "Home Address" as well as co-located care-of
address of the destination address if it happen to be mobile. The
same approach has been extended to support IP address stacking for
the source address and to support IP address stacking for both source
address as well as destination address. The "Reserved" space in the
type 2 routing header has been split into two parts; an one octet
field to address the "Stacking Type" and the rest 3 octets are left
as Reserved.
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Stacking Type is interpreted as follows:
Stacking Type=0
Source Address: Address of the sender.
Destination Address: co-located care-of address of the receiver.
Address 1: Home Address/PI Address of the receiver.
Hdr Ext Len=2.
So, type 2 routing header for stacking type 0 will be as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len=2 | Routing Type=2|Segments Left=1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Stacking Type=0| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Address 1:Home Address/PI Address of the receiver +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stacking Type=1
Source Address: co-located care-of address of the sender.
Destination address: Address of the receiver.
Address 1: Home Address/PI Address of the sender.
Hdr Ext Len=2.
So, type 2 routing header for stacking type 1 will be as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len=2 | Routing Type=2|Segments Left=1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Stacking Type=1| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Address 1:Home Address/PI Address of the sender +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stacking Type 2
Source Address: co-located care-of address of the sender.
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Destination Address: co-located care-of address of the receiver.
Address 1: Home Address/PI Address of the sender.
Address 2: Home Address/PI Address of the receiver.
Hdr Ext Len=4.
So, type 2 routing header for stacking type 2 will be as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len=4 | Routing Type=2|Segments Left=1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Stacking Type=2| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Address 1:Home Address/PI Address of the sender +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Address 2:Home Address/PI Address of the receiver +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header
8-bit selector. Identifies the type of header immediately
following the routing header. Uses the same values as the IPv6
Next Header field [9].
Hdr Ext Len
4 (8-bit unsigned integer); length of the routing header in 8-
octet units, not including the first 8 octets.
Routing Type
2 (8-bit unsigned integer).
Segments Left
1 (8-bit unsigned integer).
Stacking Type
2 (8-bit unsigned integer).
Reserved
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24-bit reserved field. The value MUST be initialized to zero by
the sender, and MUST be ignored by the receiver.
Address 1
Home Address/PI Address of the sender.
Address 2
Home Address/PI Address of the receiver.
IP address stacking in IPv4 is performed by introducing new IP option
under the option class "Datagram or Network Control", i.e. 0. The
option number is 16. The CODE(144) field is followed by one octet
field "Stacking Type" followed by two octet reserved space (NULL) as
padding followed by the address fields based on the Stacking Type.
Stacking Type is interpreted as follows:
Stacking Type=0
Source Address: Address of the sender.
Destination Address: co-located care-of address of the receiver.
Address 1: Home Address/PI Address of the receiver.
Header Length:7
Format of IP address stacking option with stacking type 0
in the IP header will be as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CODE(144) |Stacking Type=0| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Address 1:Home Address/PI Address of the receiver +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stacking Type=1
Source Address: co-located care-of address of the sender.
Destination Address: Address of the receiver.
Address 1: Home Address/PI Address of the sender.
Header Length:7
Format of IP address stacking option with stacking type 1
in the IP header will be as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CODE(144) |Stacking Type=1| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Address 1:Home Address/PI Address of the sender +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stacking Type=2
Source Address: co-located care-of address of the sender.
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Destination Address: co-located care-of address of the receiver.
Address 1: Home Address/PI Address of the sender.
Address 2: Home Address/PI Address of the receiver.
Header Length:8
Format of IP address stacking option with stacking type 2
in the IP header will be as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CODE(144) |Stacking Type=2| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Address 1:Home Address/PI Address of the sender +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Address 2:Home Address/PI Address of the receiver +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2.3. Implementation aspects
Following changes are expected with the source code of BSD.
Introduce ip_domain structure and some parameters as follows:
struct ip_domain {
struct in_addr net_addr;
struct in_addr net_mask;
struct in_addr def_router;
};
#define MAX_IP_DOMAINS 16
short num_ipdomains;
struct ip_domain *ipdomain[MAX_IP_DOMAINS];
If customer network maintains private IP domain (along with the user-
id space provided by the service providers) and expects its
communication to be confined within its own space, 'def_router' has
to be set as NULL.
Upload IP domain information for all of its IP domains during system
start up. These domain information can be uploaded through router
advertisement or through DHCP. The domain information should contain
the next hop address to reach the corresponding default router as
well.
There has to be a provision to upload these information through
'sysctl' to configure them manually.
Three new 'sysctl' routines have to be introduced under the 'ip' node
of the MIB tree (i.e. under CTL_NET, PF_INET, IPPROTO_IP)
IPCTL_NUM_DOMAINS, IPCTL_DOMAIN and IPCTL_USE_HOMEADDR (applicable
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for mobile node). Both IPCTL_NUM_DOMAINS and IPCTL_USE_HOMEADDR are
of type CTLTYPE_INT and IPCTL_DOMAIN is of type CTLTYPE_NODE. Using
'sysctl' IPCTL_NUM_DOMAINS has to be configured first. Configuration
of IPCTL_NUM_DOMAINS has to populate IPCTL_NUM_DOMAIN entries of
nodes under IPCTL_DOMAIN and for each of these nodes three MIB
attributes DOMAIN_NET_ADDR, DOMAIN_NET_MASK and DOMAIN_DEF_ROUTER
(each of type CTLTYPE_NODE) has to be allocated.
All the routers as well as hosts that are having interfaces
connecting to multiple subnets need to be configured through
'sysctl'.
Mobile users should get provision to change IPCTL_USE_HOMEADDR
attribute dynamically.
Add a route entry for all the default routers during system start up.
2.3.1. Processing of system call 'getsrcaddr'
Introduce a routine (say 'getendpointaddr') that will find out a list
of source-destination addressees sorted in order based on sending
Path messages between a list of source addresses to a list of
destination addresses. The routine should select the service type
based on the type of service field (which can be obtained by calling
'getsockopt' with the socket id 'sockfd' passed as a parameter).
System call 'getsrcaddr' has to be processed in the following manner:
If destination address of the IP packet falls outside of its
IP domains {
If user has selected its "Home Address" {
/*Applicable to IP mobility/PI address*/
return its "Home Address";
}
If destination address is from private address space {
if the host is having only one interface {
call 'getendpointaddr' for the destination address
with all the private addresses assigned to it. get source
address based on the output of 'getendpointaddr'.
}
else {
for all the default routers {
use 'rtalloc' to get the next hop address for the
default router.
select source address based on the outgoing interface
'ia', and the private address associated with the default
router.
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}
call 'getendpointaddr' for the destination address with
all the private addresses selected above. get source
address based on the output of 'getendpointaddr'.
}
}
else {
if the host is having only one interface {
call 'getendpointaddr' for the destination address
with all the global unicast addresses assigned to it. get
source addresses based on the output of 'getendpointaddr'.
}
else {
for all the default routers {
use 'rtalloc' to get the next hop address for the
default router.
select source address based on the outgoing interface
'ia', and the global unicast address associated
with the default router.
}
call 'getendpointaddr' for the destination address with
all the global unicast addresses selected above. get source
address based on the output of 'getendpointaddr'.
}
}
}
else { /* i.e. destination address is inside its IP domains */
use 'rtalloc' to get the next hop address for the
destination address.
if destination address is a link local address {
select source address based on the outgoing interface
and the link local address assigned to it.
}
else {
select source address based on the outgoing interface
and the domain that the destination address belongs to.
}
}
2.3.2. Processing of 'gethostbynamewithsrcaddr'
System call 'gethostbynamewithsrcaddr' has to be processed in the
following manner:
This is an enhancement of the system call 'gethostbyname'.
'gethostbyname' calls three routines that performs host table search,
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NIS search and DNS search. Once name is resolved, following additions
are expected to resolve source-destination pair.
If 'hostent' structure contains addresses which are inside its IP
domains {
if 'hostent' structure contains a private address {
Assign destination address as a private address
contained in 'hostent';
use 'rtalloc' to get the next hop address for the
destination address.
select source address based on the outgoing interface
and the domain that the destination address belongs to.
}
else {
Select a global unicast address contained in 'hostent' for
destination address.
use 'rtalloc' to get the next hop address for the
destination address.
select source address based on the outgoing interface
and the domain that the destination address belongs to.
}
}
else {
if 'hostent' structure contains private address {
if host is having only one interface {
call 'getendpointaddr' with all the private addresses
returned by 'gethostbyname' as destination addresses
with all the private addresses assigned to it as host
addresses and return source and destination addresses
based on its output.
}
else {
for all the default routers {
use 'rtalloc' to get the next hop address for the
default router.
select source address based on the outgoing interface
'ia', and the private address associated with the default
router.
}
call 'getendpointaddr' with all the private addresses
returned by 'gethostbyname' as destination addresses
with all the selected private addresses above as host
addresses. get source and destination addresses
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based on the output of 'getendpointaddr'.
}
}
else {
if user has selected its "Home Address" {
/*Applicable to IP mobility/PI address*/
Call 'getendpointaddr' with all the addresses returned
by 'gethostbyname' as destination addresses with the
"Home Address" and return source and destination
addresses based on its output.
}
if host is having only one interface {
Call 'getendpointaddr' with all the addresses returned
by 'gethostbyname' as destination addresses with all of its
global unicast addresses as source addresses and return
source and destination addresses based on its output.
}
else {
for all the default routers {
use 'rtalloc' to get the next hop address for the
default router.
select source address based on the outgoing interface
'ia', and the global unicast address associated
with the default router.
}
call 'getendpointaddr' with all the global unicast
addresses returned by 'gethostbyname' as destination
addresses with all the selected global unicast addresses
as host addresses. get source and destination addresses
based on the output of 'getendpointaddr'.
}
}
}
2.3.3. Changes required in ip_output and ip_forwarding modules
Execute the following steps in the 'ip_output' routine of the IP
stack before it calls 'rtalloc' for route look up.
If destination address of the IP packet falls outside of its
IP domains {
get def router address based on the IP domain
the source address belongs to.
use 'rtalloc' to get the next hop address for the def router.
Forward the packet to the next hop.
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}
else { /* i.e. destination address is inside its IP domains */
follow the usual procedure to forward packets
}
In BSD, the 'ip_forwarding' routine calls 'ip_output'; so it should
be left as it is.
2.3.4. Processing of protocol input routines and socket IO system calls
Protocol input routines need to locate the socket/process in the
usual manner with the 5 unit tuple (i.e. protocol, source address,
source port, destination address, destination port).
When a packet is received by a mobile node (at a foreign site), it
can be received in two modes. It can be received directly from the
correspondent node with the 'destination address' as the co-located
care-of address and its home address in the IP stack (see section 4.1
of RFC6275[8]). In the second mode the packet can be received via the
home agent using IP over IP. Once the IP layer receives a packet with
IP over IP, it is supposed to strip off the outer header before
passing the packet to the protocol input routine. In this case
packet will be received by the protocol input routine with
destination address as the home address of the mobile node with no
information related to its care-of address. So, protocol input
routine needs to check whether the destination address of the
received packet belongs to any one of its IP domains. If it does
not, it needs to find out the co-located care-of address by going
through the interface list if it is not already found in the packet
received. This information is needed by the TCP input routine while
processing a SYN message. It is also needed by the UDP/RAW modules
while processing the system call 'recvwithdstaddr'.
While processing the output routines like 'sendwithsrcaddr',
'sendto', UDP/RAW modules needs to check the parameters related to
source address, source port, destination address, destination port,
care-of address of the source, care-of address of the destination in
the protocol control block. Parameters in the PCB should prevail over
parameters passed by the system call while forming the IP packet.
2.4. Multihoming and VPN
For a corporate, that maintains multiple offices and communicates
within themselves through private address space using VPN needs to
distribute its entire private address space to all its site in a
suitable manner. Each one of its offices will get multiple private
address space where each of them will be associated with a particular
link. Let us consider one of its offices gets connected to two
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providers P1 and P2 and gets address space as
'unicastNetAddr1'/'unicastNetMask1' and
'unicastNetAddr2'/'unicastNetMask2' respectively. It also gets
assigned private address space from its corporate as
'privateDomainNetAddr1'/'privateDomainNetMask1' and
'privateDomainNetAddr2'/'privateDomainNetMask2' which will be
associated with the CE routers CE1 and CE2 respectively.
All hosts as well as the intermediate routers will have four entries
of ip_domain:
1: 'net_addr = 'unicastNetAddr1'
'net_mask = 'unicastNetMask1'
'def_router = CE1
2: 'net_addr = 'unicastNetAddr2'
'net_mask = 'unicastNetMask2'
'def_router = CE2
3: 'net_addr' = 'privateDomainNetAddr1'
'net_mask' = 'privateDomainNetMask1'
'def_router' = CE1
4: 'net_addr' = 'privateDomainNetAddr2'
'net_mask' = 'privateDomainNetMask2'
'def_router' = CE2
3. Security Consideration
This document provides a solution for site multihoming of stub
networks. Message exchange between source and destination related to
link failure has to be done in secured mode as explained in section
2.1.2. For common security related issues that any site may
experience, one needs to consult with the "Site Security Handbook",
RFC2196[6]. For issues related to IP Mobility, section 5 of
RFC5944[4] has to be consulted.
4. IANA Consideration
This draft does not request any action from IANA.
5. Normative References
[1] J. Abley, B. Black, V. Gill, "Goals for IPv6 Site-Multihoming
Architectures", RFC3582, August 2003.
[2] R. Braden, "Requirements for Internet Hosts -- Communication
Layers", RFC1122, October 1989.
[3] R. Hinden, S. Deering, "IP Version 6 Addressing Architecture.",
RFC4291, February 2006.
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[4] C. Perkins, "IP Mobility Support for IPv4, Revised", RFC5944,
November 2010.
[5] T. Dierks, E. Rescorla, "The Transport Layer Security (TLS)
Protocol Version 1.2", RFC5246, August 2008.
[6] B. Fraser, "Site Security Handbook", RFC2196, September 1997.
[7] S. Bandyopadhyay, "An Architectural Framework of the Internet
for the Real IP World" <draft-shyam-real-ip-framework-24.txt>
(work in progress).
[8] C. Perkins, Ed., D. Johnson, J. Arkko, "Mobility Support in
IPv6" RFC 6275, July 2011.
[9] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[10] L. Zhang, S. Berson, S. Herzog, S. Jamin, "Resource ReSerVation
Protocol (RSVP) -- Version 1 Functional Specification", RFC
2205, September 1997.
[11] D. Awduche, L. Berger, D. Gan, T. Li, V. Srinivasan, G.
Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels",
RFC 3209, December 2001.
[12] G. Swallow, J. Drake, H. Ishimatsu, Y. Rekhter, "Generalized
Multiprotocol Label Switching (GMPLS) User-Network Interface
(UNI): Resource ReserVation Protocol-Traffic Engineering
(RSVP-TE) Support for the Overlay Model", RFC 4208,
October 2005.
[13] J. Wroclawski, "Specification of the Controlled-Load Network
Element Service", RFC 2211, September 1997.
[14] S. Shenker, C. Partridge, R. Guerin, "Specification of
Guaranteed Quality of Service", RFC 2212, September 1997.
6. Informative References
[15] P. Srisuresh, K. Egevang, "Traditional IP Network Address
Translator (Traditional NAT)", RFC3022, January 2001.
7. Author's Address
Shyamaprasad Bandyopadhyay
HL No 205/157/7, Kharagpur 721305, India
Phone: +91 3222 225137
e-mail: shyamb66@gmail.com
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