INTERNET-DRAFT Mingui Zhang
Intended Status: Proposed Standard Donald Eastlake
Huawei
Radia Perlman
EMC
Margaret Wasserman
Painless Security
Hongjun Zhai
JIT
Expires: January 7, 2016 July 6, 2015
Single Area Border RBridge Nickname for TRILL Multilevel
draft-zhang-trill-multilevel-single-nickname-01.txt
Abstract
A major issue in multilevel TRILL is how to manage RBridge nicknames.
In this document, the area border RBridge uses a single nickname in
both Level 1 and Level 2. RBridges in Level 2 must obtain unique
nicknames but RBridges in different Level 1 areas may have the same
nicknames.
Status of this Memo
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Copyright and License Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Acronyms and Terminology . . . . . . . . . . . . . . . . . . . 3
2.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Nickname Handling on Border RBridges . . . . . . . . . . . . . 3
3.1. Actions on Unicast Packets . . . . . . . . . . . . . . . . 4
3.2. Actions on Multi-Destination Packets . . . . . . . . . . . 5
4. Per-flow Load Balancing . . . . . . . . . . . . . . . . . . . . 6
4.1. Ingress Nickname Replacement . . . . . . . . . . . . . . . 6
4.2. Egress Nickname Replacement . . . . . . . . . . . . . . . . 7
5. Protocol Extensions for Discovery . . . . . . . . . . . . . . . 7
5.1. Discovery of Border RBridges in L1 . . . . . . . . . . . . 7
5.2. Discovery of Border RBridge Sets in L2 . . . . . . . . . . 8
6. One Border RBridge Connects Multiple Areas . . . . . . . . . . 8
7. E-L1FS/E-L2FS Backwards Compatibility . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 9
9.1. TRILL APPsub-TLVs . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . . 10
Appendix A. Clarifications . . . . . . . . . . . . . . . . . . . . 10
A.1. Level Transition . . . . . . . . . . . . . . . . . . . . . 11
Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
TRILL multilevel techniques are designed to improve TRILL scalability
issues. As described in [MultiL], there have been two proposed
approaches. One approach, which is referred as the "unique nickname"
approach, gives unique nicknames to all the TRILL switches in the
multilevel campus, either by having the Level-1/Level-2 border TRILL
switches advertise which nicknames are not available for assignment
in the area, or by partitioning the 16-bit nickname into an "area"
field and a "nickname inside the area" field. The other approach,
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which is referred as the "aggregated nickname" approach, involves
assigning nicknames to the areas, and allowing nicknames to be reused
in different areas, by having the border TRILL switches rewrite the
nickname fields when entering or leaving an area.
The approach specified in this document is different from both
"unique nickname" and "aggregated nickname" approach. In this
document, the nickname of an area border RBridge is used in both
Level 1 (L1) and Level 2 (L2). No additional nicknames are assigned
to the L1 areas. Each L1 area is denoted by the group of all
nicknames of those border RBridges of the area. For this approach,
nicknames in L2 MUST be unique but nicknames inside different L1
areas MAY be reused. The use of the approach specified in this
document in one L1 area does not prohibit the use of other approaches
in other L1 areas in the same TRILL campus.
2. Acronyms and Terminology
2.1. Acronyms
Data Label: VLAN or FGL
IS-IS: Intermediate System to Intermediate System [ISIS]
2.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Familiarity with [RFC6325] is assumed in this document.
3. Nickname Handling on Border RBridges
This section provides an illustrative example and description of the
border learning border RBridge nicknames.
Area {2,20} level 2 Area {3,30}
+-------------------+ +-----------------+ +--------------+
| | | | | |
| S--RB27---Rx--Rz----RB2---Rb---Rc--Rd---Re--RB3---Rk--RB44---D |
| 27 | | | | 44 |
| ----RB20--- ----RB30--- |
+-------------------+ +-----------------+ +--------------+
Figure 3.1: An example topology for TRILL multilevel
In Figure 3.1, RB2, RB20, RB3 and RB30 are area border TRILL switches
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(RBridges). Their nicknames are 2, 20, 3 and 30 respectively. Area
border RBridges use the set of border nicknames to denote the L1 area
that they are attached to. For example, RB2 and RB20 use nicknames
{2,20} to denote the L1 area on the left.
A source S is attached to RB27 and a destination D is attached to
RB44. RB27 has a nickname, say 27, and RB44 has a nickname, say 44
(and in fact, they could even have the same nickname, since the TRILL
switch nickname will not be visible outside these Level 1 areas).
3.1. Actions on Unicast Packets
Let's say that S transmits a frame to destination D and let's say
that D's location is learned by the relevant TRILL switches already.
These relevant switches have learned the following:
1) RB27 has learned that D is connected to nickname 3.
2) RB3 has learned that D is attached to nickname 44.
The following sequence of events will occur:
- S transmits an Ethernet frame with source MAC = S and destination
MAC = D.
- RB27 encapsulates with a TRILL header with ingress RBridge = 27,
and egress RBridge = 3 producing a TRILL Data packet.
- RB2 and RB20 have announced in the Level 1 IS-IS instance in area
{2,20}, that they are attached to all those area nicknames,
including {3,30}. Therefore, IS-IS routes the packet to RB2 (or
RB20, if RB20 on the least-cost route from RB27 to RB3).
- RB2, when transitioning the packet from Level 1 to Level 2,
replaces the ingress TRILL switch nickname with its own nickname,
so replaces 27 with 2. Within Level 2, the ingress RBridge field
in the TRILL header will therefore be 2, and the egress RBridge
field will be 3. (The egress nickname MAY be replaced with an area
nickname selected from {3,30}. See Section 4 for the detail of the
selection method. Here, suppose nickname 3 is used.) Also RB2
learns that S is attached to nickname 27 in area {2,20} to
accommodate return traffic. RB2 SHOULD synchronize with RB20 using
ESADI protocol [RFC7357] that MAC = S is attached to nickname 27.
- The packet is forwarded through Level 2, to RB3, which has
advertised, in Level 2, its L2 nickname as 3.
- RB3, when forwarding into area {3,30}, replaces the egress
nickname in the TRILL header with RB44's nickname (44). (The
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ingress nickname MAY be replaced with an area nickname selected
from {2,20}. See Section 4 for the detail of the selection method.
Here, suppose nickname 2 is selected.) So, within the destination
area, the ingress nickname will be 2 and the egress nickname will
be 44.
- RB44, when decapsulating, learns that S is attached to nickname 2,
which is one of the area nicknames of the ingress.
3.2. Actions on Multi-Destination Packets
Distribution trees for flooding of multi-destination packets are
calculated separately within each L1 area and L2. When a multi-
destination packet arrives at the border, it needs to be transitioned
either from L1 to L2, or from L2 to L1. All border RBridges are
eligible for Level transition. However, for each multi-destination
packet, only one of them acts as the Designated Border RBridge (DBRB)
to do the transition while other non-DBRBs MUST drop the received
copies. All border RBridges of an area SHOULD agree on a pseudorandom
algorithm and locally determine the DBRB as they do in the "Per-flow
Load Balancing" section. It's also possible to implement a certain
election protocol to elect the DBRB. However, such kind of
implementations are out the scope of this document.
As per [RFC6325], multi-destination packets can be classified into
three types: unicast packet with unknown destination MAC address
(unknown-unicast packet), multicast packet and broadcast packet. Now
suppose that D's location has not been learned by RB27 or the frame
received by RB27 is recognized as broadcast or multicast. What will
happen, as it would in TRILL today, is that RB27 will forward the
packet as multi-destination, setting its M bit to 1 and choosing an
L1 tree, flooding the packet on the distribution tree, subject to
possible pruning.
When the copies of the multi-destination packet arrive at area border
RBridges, non-DBRBs MUST drop the packet while the DBRB, say RB2,
needs to do the Level transition for the multi-destination packet.
For a unknown-unicast packet, if the DBRB has learnt the destination
MAC address, it SHOULD convert the packet to unicast and set its M
bit to 0. Otherwise, the multi-destination packet will continue to be
flooded as multicast packet on the distribution tree. The DBRB
chooses the new distribution tree by replacing the egress nickname
with the new root RBridge nickname. The following sequence of events
will occur:
- RB2, when transitioning the packet from Level 1 to Level 2,
replaces the ingress TRILL switch nickname with its own nickname,
so replaces 27 with 2. RB2 also needs to replace the egress
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RBridge nickname with the L2 tree root RBridge nickname, say 2. In
order to accommodate return traffic, RB2 records that S is
attached to nickname 27 and SHOULD use ESADI protocol to
synchronize this attachment information with other border RBridges
(say RB20) in the area.
- RB20, will receive the packet flooded on the L2 tree by RB2. It is
important that RB20 does not transition this packet back to L1 as
it does for a multicast packet normally received from another
remote L1 area. RB20 should examine the ingress nickname of this
packet. If this nickname is found to be a border RBridge nickname
of the area {2,20}, RB2 must not forwarded the packet into this
area.
- The packet is flooded on the Level 2 tree to reach both RB3 and
RB30. Suppose RB3 is the selected DBRB. The non-DBRB RB30 will
drop the packet.
- RB3, when forwarding into area {3,30}, replaces the egress
nickname in the TRILL header with the root RBridge nickname, say
3, of the distribution tree of L1 area {3,30}. (Here, the ingress
nickname MAY be replaced with an area nickname selected from
{2,20} as specified in Section 4.) Now suppose that RB27 has
learned the location of D (attached to nickname 3), but RB3 does
not know where D is. In that case, RB3 must turn the packet into a
multi-destination packet and floods it on the distribution tree of
L1 area {3,30}.
- RB30, will receive the packet flooded on the L1 tree by RB3. It is
important that RB30 does not transition this packet back to L2.
RB30 should also examine the ingress nickname of this packet. If
this nickname is found to be an L2 border RBridge nickname, RB30
must not transition the packet back to L2.
- The multicast listener RB44, when decapsulating the received
packet, learns that S is attached to nickname 2, which is one of
the area nicknames of the ingress.
4. Per-flow Load Balancing
Area border RBridges perform ingress/egress nickname replacement when
they transition TRILL data packets between Level 1 and Level 2. This
nickname replacement enables the per-flow load balance which is
specified as follows.
4.1. Ingress Nickname Replacement
When a TRILL data packet from other areas arrives at an area border
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RBridge, this RBridge MAY select one area nickname of the ingress to
replace the ingress nickname of the packet. The selection is simply
based on a pseudorandom algorithm as defined in Section 5.3 of
[RFC7357]. With the random ingress nickname replacement, the border
RBridge actually achieves a per-flow load balance for returning
traffic.
All area border RBridges in an L1 area MUST agree on the same
pseudorandom algorithm. The source MAC address, ingress area
nicknames, egress area nicknames and the Data Label of the received
TRILL data packet are candidate factors of the input of this
pseudorandom algorithm. Note that the value of the destination MAC
address SHOULD be excluded from the input of this pseudorandom
algorithm, otherwise the egress RBridge will see one source MAC
address flip flopping among multiple ingress RBridges.
4.2. Egress Nickname Replacement
When a TRILL data packet originated from the area arrives at an area
border RBridge, this RBridge MAY select one area nickname of the
egress to replace the egress nickname of the packet. By default, it
SHOULD choose the egress area border RBridge with the least cost
route to reach. The pseudorandom algorithm as defined in Section 5.3
of [RFC7357] may be used as well. In that case, however, the ingress
area border RBridge may take the non-least-cost Level 2 route to
forward the TRILL data packet to the egress area border RBridge.
5. Protocol Extensions for Discovery
5.1. Discovery of Border RBridges in L1
The following Level 1 Border RBridge APPsub-TLV will be included in
an E-L1FS FS-LSP fragment zero [RFC7180bis] as an APPsub-TLV of the
TRILL GENINFO-TLV. Through listening to this Appsub-TLV, an area
border RBridge discovers all other area border RBridges in this area.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = L1-BORDER-RBRIDGE | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Nickname | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: Level 1 Border RBridge (TRILL APPsub-TLV type tbd1)
o Length: 2
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o Sender Nickname: The nickname the originating IS will use as the
L1 Border RBridge nickname. This field is useful because the
originating IS might own multiple nicknames.
5.2. Discovery of Border RBridge Sets in L2
The following APPsub-TLV will be included in an E-L2FS FS-LSP
fragment zero [RFC7180bis] as an APPsub-TLV of the TRILL GENINFO-TLV.
Through listening to this APPsub-TLV in L2, an area border RBridge
discovers all groups of L1 border RBridges and each such group
identifies an area.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = L1-BORDER-RB-GROUP | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L1 Border RBridge Nickname 1 | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L1 Border RBridge Nickname k | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: Level 1 Border RBridge Group (TRILL APPsub-TLV type tbd2)
o Length: 2*k. If length is not a multiple of 2, the APPsub-TLV is
corrupt and MUST be ignored.
o L1 Border RBridge Nickname: The nickname that an area border
RBridge uses as the L1 Border RBridge nickname. The L1-BORDER-RB-
GROUP TLV generated by an area border RBridge MUST include all L1
Border RBridge nicknames of the area. It's RECOMMENDED that these
k nicknames are ordered in ascending order according to the 2-
octet nickname considered as an unsigned integer.
When an L1 area is partitioned [MultiL], border RBridges will re-
discover each other in both L1 and L2 through exchanging LSPs. In L2,
the set of border RBridge nicknames for this splitting area will
change. Border RBridges that detect such a change MUST flush the
reach-ability information associated to any RBridge nickname from
this changing set.
6. One Border RBridge Connects Multiple Areas
It's possible that one border RBridge (say RB1) connects multiple L1
areas. RB1 SHOULD use a single area nickname for all these areas.
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Nicknames used within one of these areas can be reused within other
areas. It's important that packets destined to those duplicated
nicknames are sent to the right area. Since these areas are connected
to form a layer 2 network, duplicated {MAC, Data Label} across these
areas ought not occur. Now suppose a TRILL data packet arrives at the
area border nickname of RB1. For a unicast packet, RB1 can lookup the
{MAC, Data Label} entry in its MAC table to identify the right
destination area (i.e., the outgoing interface) and the egress
RBridge's nickname. For a multicast packet: suppose RB1 is not the
DBRB, RB1 will not transition the packet; otherwise, RB1 is the DBRB,
- if this packet is originated from an area out of the connected
areas, RB1 should replicate this packet and flood it on the proper
Level 1 trees of all the areas in which it acts as the DBRB.
- if the packet is originated from one of the connected areas, RB1
should replicate the packet it receives from the Level 1 tree and
flood it on other proper Level 1 trees of all the areas in which
it acts as the DBRB except the originating area (i.e., the area
connected to the incoming interface). RB1 may also receive the
replication of the packet from the Level 2 tree. This replication
must be dropped by RB1.
7. E-L1FS/E-L2FS Backwards Compatibility
All Level 2 RBridges MUST support E-L2FS [RFC7356] [rfc7180bis]. The
Extended TLVs defined in Section 5 are to be used in Extended Level
1/2 Flooding Scope (E-L1FS/E-L2FS) PDUs. Area border RBridges MUST
support both E-L1FS and E-L2FS. RBridges that do not support either
E-L1FS or E-L2FS cannot serve as area border RBridges but they can
well appear in an L1 area acting as non-area-border RBridges.
8. Security Considerations
For general TRILL Security Considerations, see [RFC6325].
The newly defined TRILL APPsub-TLVs in Section 5 are transported in
IS-IS PDUs whose authenticity can be enforced using regular IS-IS
security mechanism [ISIS][RFC5310]. This document raises no new
security issues for IS-IS.
9. IANA Considerations
9.1. TRILL APPsub-TLVs
IANA is requested to allocate two new types under the TRILL GENINFO
TLV [RFC7357] for the TRILL APPsub-TLVs defined in Section 5. The
following entries are added to the "TRILL APPsub-TLV Types under IS-
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IS TLV 251 Application Identifier 1" Registry on the TRILL Parameters
IANA web page.
Type Name Reference
--------- ---- ---------
tbd1[256] L1-BORDER-RBRIDGE [This document]
tbd2[257] L1-BORDER-RB-GROUP [This document]
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, July 2011.
[RFC7356] L. Ginsberg, S. Previdi, et al, "IS-IS Flooding Scope
LSPs", RFC 7356, June 2014.
[RFC7357] Zhai, H., Hu, F., Perlman, R., Eastlake 3rd, D., and O.
Stokes, "Transparent Interconnection of Lots of Links
(TRILL): End Station Address Distribution Information
(ESADI) Protocol", RFC 7357, September 2014.
10.2. Informative References
[ISIS] ISO, "Intermediate system to Intermediate system routeing
information exchange protocol for use in conjunction with
the Protocol for providing the Connectionless-mode Network
Service (ISO 8473)", ISO/IEC 10589:2002.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic Authentication",
RFC 5310, February 2009.
[RFC7180bis] D. Eastlake, M. Zhang, et al, "TRILL: Clarifications,
Corrections, and Updates", draft-eastlake-trill-rfc7180bis,
work in progress.
[MultiL] Perlman, R., Eastlake, D., et al, "Flexible Multilevel
TRILL", draft-perlman-trill-rbridge-multilevel, work in
progress.
Appendix A. Clarifications
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A.1. Level Transition
It's possible that an L1 RBridge is only reachable from a non-DBRB
RBridge. If this non-DBRB RBridge refrains from Level transition, the
question is, how can a multicast packet reach this L1 RBridge? The
answer is, it will be reached after the DBRB performs the Level
transition and floods the packet using an L1 distribution tree.
Take the following figure as an example. RB77 is reachable from the
border RBridge RB30 while RB3 is the DBRB. RB3 transitions the
multicast packet into L1 and floods the packet on the distribution
tree rooted from RB3. This packet will finally flooded to RB77 via
RB30.
Area{3,30}
+--------------+ (root) RB3 o
| | \
-RB3 | | o RB30
| | | /
-RB30-RB77 | RB77 o
+--------------+
Example Topology L1 Tree
In the above example, the multicast packet is forwarded along a non-
optimal path. A possible improvement is to have RB3 configured not to
belong to this area. In this way, RB30 will surely act as the DBRB to
do the Level transition.
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Author's Addresses
Mingui Zhang
Huawei Technologies
No.156 Beiqing Rd. Haidian District,
Beijing 100095 P.R. China
EMail: zhangmingui@huawei.com
Donald E. Eastlake, 3rd
Huawei Technologies
155 Beaver Street
Milford, MA 01757 USA
Phone: +1-508-333-2270
EMail: d3e3e3@gmail.com
Radia Perlman
EMC
2010 256th Avenue NE, #200
Bellevue, WA 98007 USA
EMail: radia@alum.mit.edu
Margaret Wasserman
Painless Security
EMail: mrw@painless-security.com
Hongjun Zhai
Jinling Institute of Technology
99 Hongjing Avenue, Jiangning District
Nanjing, Jiangsu 211169 China
EMail: honjun.zhai@tom.com
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