Network Working Group A. Bashandy
Internet Draft Cisco Systems
Intended status: Standards Track July 10, 2011
Expires: January 2012
Scalable BGP FRR Protection against Edge Node Failure
draft-bashandy-bgp-edge-node-frr-00.txt
Abstract
Consider a BGP free core scenario. Suppose the edge BGP speakers PE1,
PE2,..., PEn know about a prefix P/p via the external routers CE1,
CE2,..., CEm. If the edge router PEi crashes or becomes totally
disconnected from the core, it desirable for a penultimate hop route
''P '' carrying traffic to the failed edge router PEi to immediately
restore traffic by re-tunneling packets originally tunneled to PEi
and destined to the prefix P/p to one of the other edge routers that
advertised P/p, say PEj, until BGP re-converges. In doing so, it is
highly desirable to keep the core BGP-free while not imposing
restrictions on external connectivity. Thus (1) a core router should
not be required to learn any BGP prefix, (2) the size of the
forwarding and routing tables in the core routers should be
independent of the number of BGP prefixes,(3) there should be no
special router (or group of routers) that handles restoring traffic,
and (4) there should be no restrictions on what edge routers
advertise what prefixes. For labeled prefixes, (5) the penultimate
hop router must swap the label advertised by the failed edge router
PEi for the prefix P/p with the label advertised for the same prefix
by the edge router PEj before re-tunneling the packet to PEj
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Table of Contents
1. Introduction...................................................3
1.1. Problem definition........................................4
1.2. Conventions used in this document.........................5
1.3. Terminology...............................................5
2. Control Plane Operation........................................6
2.1. Control plane Operation for unlabeled prefixes............6
2.1.1. Step 1: Calculation of the Repair PE.................7
2.1.2. Step 2: Assigning and Advertising the BGP Next-hop...7
2.1.3. Step 3: Informing Core Routers about the Repair PE...7
2.1.4. Step 4: How a P router (a core router) Programs its
Forwarding Plane............................................8
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2.2. Control plane Operation for Labeled Prefixes..............8
2.2.1. Step 1: Calculation of the Repair PE.................9
2.2.2. Step 2: Assigning and Advertising the BGP Next-hop...9
2.2.3. Step 3: Informing core routers about the repair path.9
2.2.4. Step 4: How a P router (a core router) programs its
forwarding plane...........................................10
2.3. Rules for a choosing Repair path.........................11
2.3.1. General Rules for Choosing and Programming the Repair
Path.......................................................11
2.3.2. Rules for Choosing the Repair Path for Labeled Prefixes
...........................................................11
2.4. Forwarding Plane Operation...............................12
2.4.1. For unlabeled prefix................................12
2.4.2. For Labeled prefix..................................13
3. Example.......................................................14
4. Security Considerations.......................................16
5. IANA Considerations...........................................16
6. Conclusions...................................................16
7. References....................................................16
7.1. Normative References.....................................16
7.2. Informative References...................................16
8. Acknowledgments...............................................17
1. Introduction
In a BGP free core, where traffic is tunneled between edge routers,
BGP speakers advertise reachability information about prefixes. For
labeled address families, namely AFI/SAFI 1/4, 2/4, 1/128, and
2/128, an edge router assigns local labels to prefixes and
associates the local label with each advertised prefix such as
L3VPN [ .6], 6PE . [7], and Softwire [ .5]. Suppose that a given edge
router is chosen as the best next-hop for a prefix P/p. An ingress
router that receives a packet from an external router and destined
for the prefix P/p "tunnels" the packet across the core to that
egress router. If the prefix P/p is a labeled prefix, the ingress
router pushes the label advertised by the egress router before
tunneling the packet to the egress router. Upon receiving the
packet from the core, the egress router takes the appropriate
forwarding decision based on the content of the packet or the label
pushed on the packet.
In modern networks, it is not uncommon to have a prefix reachable
via multiple edge routers. One example is the best external path
[ .4]. Another more common and widely deployed scenario is L3VPN [ .6]
with multi-homed VPN sites. As an example, consider the L3VPN
topology depicted in F .igure 1.
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PE1
\
\
\
\
CE1....... VPN prefix
/ (10.0.0.0/8)
/
/
/
BGP free core P--------PE0
\
\
\
\
CE2....... VPN prefix
/ (20.0.0.0/8)
/
/
/
PE2
Figure 1 VPN prefix reachable via multiple PEs
As illustrated in F .igure 1, the edge router PE0 is the primary NH
for both 10.0.0.0/8 and 20.0.0.0/8. At the same time, both
10.0.0.0/8 and 20.0.0.0/8 are reachable through the other edge
routers PE1 and PE2, respectively.
1.1. Problem definition
The problem that we are trying to solve is as follows
o Even though multiple prefixes may share the same egress router,
they have different backup edge router. In F .igure 1 above, both
10.0.0.0/8 and 20.0.0.0/8 share the same primary next hop PE0,
the routing protocol(s) must identify that the node protecting
loop free alternate for 10.0.0.0/8 is PE1 while the node
protecting loop free alternate for 11.0.0.0/8 is PE2
o On loosing connection to the edge router, the core router "P"
needs to redirect traffic towards the "correct" backup edge
router without waiting for IGP or BGP to re-converge and update
the routing tables. On the failure of PE0 illustrated in . Figure
1, the core router P MUST reroute traffic for 10.0.0.0/8 towards
PE1 and traffic for 11.0.0.0/8 towards PE2
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o The core router P MUST NOT be forced to learn about the BGP
prefixes on any of the edge routers. The same applies for all
core routers.
o There SHOULD NOT be a need for a special router or group of
routers to handle rerouting traffic on edge node failure.
o The size of the routing table on any core router MUST be
independent of the number of BGP prefixes in the network.
o For labeled prefixes, the core router MUST swap the label
advertised by egress edge router (PE0 in F .igure 1) with the
label advertised by the backup router (PE1 and PE2 in F .igure 1).
1.2. Conventions used in this document
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 [ .1].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
1.3. Terminology
This section outlines the terms used in this document. For ease of
use, we will use terms similar to those used by L3VPN [ .6]
o BGP-Free core: A network where BGP prefixes are only known to
the edge routers and traffic is tunneled between edge routers
o Protected prefix: It is a prefix P/p (of any AFI) that a BGP
speaker has an external path to. The BGP speaker may learn about
the prefix from an external peer through BGP, some other
protocol, or manual configuration. The protected prefix is
advertised to some or all the internal peers.
o Primary egress PE: It is an IBGP peer that can reach the
protected prefix P/p through an external path and advertised the
prefix to the other IBGP peers. The primary egress PE was chosen
as the best path by one or more internal peers. In other words,
the primary egress PE is an egress PE that will normally be used
by some ingress PEs when there is no failure. Referring to
F .igure 1, PE0 is a primary egress PE.
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o Primary next-hop: It is an IPv4 or IPv6 host address belonging
to the primary egress PE. If the prefix is advertised via BGP,
then the primary next-hop is the next-hop attribute in the BGP
update message [ .2]. [3].
o CE: It is an external router through which an egress PE can
reach a prefix P/p. The routers "CE1" and "CE2" in F .igure 1 are
examples of such CE.
o Ingress PE: It is a BGP speaker that learns about a prefix
through another IBGP peer and chooses that IBGP peer as the
next-hop for the prefix.
o Repairing P router: A core router that attempts to restore
traffic when the primary egress PE is no longer reachable
without waiting for IGP or BGP to re-converge. The repairing P
router restores the traffic by rerouting the traffic (through a
tunnel) towards the pre-calculated repair PE when it detects
that the primary egress PE is no longer reachable. Referring to
F .igure 1, the router "P" is the repairing P router.
o Repair egress PE: It is an egress PE other than the primary
egress PE that can reach the protected prefix P/p through an
external neighbor. The repair PE is pre-calculated via other PEs
prior to any failure. Referring to F .igure 1, PE1 is the repair
PE for 10.0.0.0/8 while PE2 is the repair PE for 20.0.0.0/8.
o Protected egress PE: Any primary egress PE protected by a
repairing P router.
o Protected edge router: Any protected egress PE.
o Repair path: It is the repair egress PE. If the protected prefix
is a labeled prefix, the repair path is the repair egress PE
together with the label that will be pushed when the repairing P
router reroutes traffic to the repair PE.
2. Control Plane Operation
This section specifies the control plane operation needed to solve
the problem mentioned in the Introduction.
2.1. Control plane Operation for unlabeled prefixes
This section specifies the operation of the control plane for
AFI/SAFI 1/1, 2/1, 1/2, and 2/2
The control plane operation can be summarized in 4 steps:
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1. Calculation of the repair PE
2. Assigning and advertising the next-hop for protected prefixes
3. Informing core routers about repair PEs
4. How a P router (a core router) programs its forwarding plane
2.1.1. Step 1: Calculation of the Repair PE
1. Consider the prefix P/p learnt by an egress edge router PEi via
an external neighbor. The edge router advertises the prefix P/p
to some or all of its IBGP peers
2. The edge router PEi MAY choose a repair PE for the external
prefix P/p. Section 2 ..3. specifies the rules for choosing the
repair edge router PEj.
3. In the end, an egress edge route PEi will have a repair edge
router PEj for some or all prefixes that PEi has external
path(s) to.
2.1.2. Step 2: Assigning and Advertising the BGP Next-hop
1. An edge router PEi groups the set of prefixes that have a repair
PE as follows: Two prefixes belong to the same group if they
share the same repair PE
2. For each group, the PE assigns a local next-hop. Thus if a
prefix P/p belongs to group Gi, its primary next-hop is NHi. For
example, the PE assigns a different loopback interface address
as the next-hop for each of the groups of prefixes.
3. When advertising the prefix and its primary next-hop to its IBGP
peers, the PE router uses NHi as the next-hop attribute of
prefixes belonging to the group Gi
2.1.3. Step 3: Informing Core Routers about the Repair PE
1. In step 2 (Section 2 ..1.2. ) the egress PE assigns a primary
next-hop NHi for protected prefixes belonging to group Gi.
2. The primary next-hop NHi is advertised to the core using IGP as
usual
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3. The repair next-hop is the next-hop attribute advertised for the
prefix P/p by the repair edge router PEj. Let's denote the
repair next-hop for prefixes belonging to group Gi by "rNHi".
Because rNHi is the next-hop advertised by the repair PE, rNHi
will also be known to all core routers via IGP
4. The egress PE MUST advertise the pair (NHi,rNHi) to all directly
connected core routers.
5. The egress PE MAY advertise the pair (NHi,rNHi) to all core
routers in the network.
6. The structure and method of advertising the pair (NHi,rNHi) is
beyond the scope of this document. For example, the pair
(NHi,rNHi) may be advertised through an ISIS optional TLV.
7. The semantics of the pair (NHi,rNHi) are: If the next-hop NHi
becomes unreachable, then traffic destined to the next-hop NHi
SHOULD be re-tunneled to the next-hop rNHi because rNHi can
reach prefixes reachable via the primary next-hop NHi.
8. Because of the previous steps, core routers that are directly
connected to the egress PE (and possibly other core routers) are
aware of the repair next-hop for protected BGP prefixes
reachable via the egress PE. Note that a core router is totally
unaware of the BGP prefixes.
2.1.4. Step 4: How a P router (a core router) Programs its Forwarding
Plane
1. Through usual IGP mechanism, the P router has a prefix matching
every BGP next-hop. Let the next-hop NHi match the route Ri
2. The next-hop of prefix Ri is on the path towards the primary
egress PE.
3. Thus the FIB entry for Ri is programmed as follows:
a. Primary next-hop: the next router on the path towards NHi
b. Repair next-hop: the next-router on the path towards rNHi
2.2. Control plane Operation for Labeled Prefixes
This section specifies the operation of the control plane for
AFI/SAFI 1/4, 2/4, 1/128, and 2/128.
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2.2.1. Step 1: Calculation of the Repair PE
1. As usual, each PE allocates a local label for each prefix it can
reach through an external neighbor CE. A PE may also allocate a
repair label is specified in [ .11].
2. Each edge router advertises the prefix together with the local
label and possibly the repair label [ .11] to some or all of its
IBGP peers.
3. As a result, an edge router PEi having an external path to the
prefix P/p may learn about the prefix through other IBGP peers.
4. The edge router PEi MAY choose a repair PE for the external
prefix P/p. Rules for choosing the repair PE are specified in
Section 2 ..3.
5. The edge router PEi chooses the one of labels advertised by the
other edge router PEj for the prefix P/p as the "repair label".
The algorithm for choosing the repair label is specified in
Section 2 ..3.
6. In the end, if the edge router PEi can reach the prefix P/p
through and external path and the prefix P/p is advertised by at
least one other PE, the edge router PEi will have
o a primary path towards the CE from which it learnt the
prefix, and
o a repair path consisting of a repair PE and a repair label
advertised by the chosen repair PE.
2.2.2. Step 2: Assigning and Advertising the BGP Next-hop
1. The edge router PEi groups all BGP prefixes for which PEi has an
external path and a repair path as follows: Two prefixes belong
to the same group Gi if they share the same repair PE and repair
label
2. The remaining steps are identical to the steps used by unlabeled
prefixes in section 2 ..1.2.
2.2.3. Step 3: Informing core routers about the repair path
1. In step 2 (Section 2 ..2.2. ) the egress PE assigns a primary
next-hop NHi and a repair path (consisting of a repair next-hop
and repair label) for protected prefixes belonging to group Gi.
2. The primary next-hop NHi is advertised into IGP as usual
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3. The repair next-hop is the next-hop advertised for the prefix
P/p by the repair edge router PEj. Denote the repair next-hop
for prefixes belonging to group Gi by "rNHi". Denote the repair
label for prefixes belonging to group Gi by "rLi". Because rNHi
is the next-hop attribute advertised by the repair PE, rNHi will
also be known to all core routers via IGP
4. The repairing egress PE MUST advertise the triplet (NHi, rNHi,
rLi) to all directly connected core routers.
5. The repairing egress PE MAY advertise the triplet (NHi, rNHi,
rLi) to all core routers in the network
6. The triplet (NHi,rNHi, rLi) may be advertised through various
means, such as ISIS optional TLV. The structure and method of
advertising the triplet (NHi,rNHi,rLi) is beyond the scope of
this document.
7. The semantics of the pair (NHi,rNHi,rLi) are: If the next-hop
NHi becomes unreachable, then traffic destined to the next-hop
NHi should be re-tunneled to the next-hop rNHi and the label
pushed by the ingress PE MUST be swapped with the label rLi
8. Because of the previous steps, core routers that are directly
connected to the egress edge router (and possibly other core
routers) are aware of the repair path for protected BGP prefixes
reachable via the egress edge router. Note that a core router is
totally unaware of the BGP prefixes themselves
2.2.4. Step 4: How a P router (a core router) programs its forwarding
plane
1. Through usual IGP mechanism, the P router has a prefix matching
every BGP next-hop. Let the primary next-hop NHi match the route
Ri
2. The next-hop of prefix Ri is on the path towards the protected
egress edge router PEi. The next-hop of the prefix Ri is
considered the primary path for the prefix Ri
3. Thus the FIB entry for Ri is programmed as follows
a. Primary path: the next router on the path towards NHi
b. Repair path:
i. Pop label in the packet right under the tunnel header
(irrespective of the value of that label)
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ii. Push the repair label rLi
iii. Re-tunnel the packet towards the repair next-hop rNHi
2.3. Rules for a choosing Repair path
This section specifies rules governing how an egress edge router
PEi chooses the repair path. Other than the rules in this section,
the method of choosing the repair path is beyond the scope of this
document.
2.3.1. General Rules for Choosing and Programming the Repair Path
This section specifies general rules for choosing the repair path
for both labeled and unlabeled prefixes.
1. A repair PE MUST be another edge router PEj that advertises the
same prefix to the edge router PEi via IBGP peering.
2. If the repairing "P" router determines that the path taken by
the tunnel from the repairing "P" router to repair edge router
PEj passes through the protected edge router PEi, then the
repairing router "P" SHOULD NOT install the repair path in its
forwarding plane. Instead the repair path MAY use a different
FRR protection mechanism such as that specified in [ .8], [ .9], and
[ .10].
The reason for this rule is that the tunnel to the repair edge
router PEj does not provide protection against the failure of
the edge node PEi. Instead it provides core protection against
the failure of the path through the core leading to the
protected edge node PEi. Thus existing core FRR protection
mechanisms such as those specified in [ .8], [ .9], and [ .10] can be
used
2.3.2. Rules for Choosing the Repair Path for Labeled Prefixes
This section specifies additional rules by which an egress edge
router PEi chooses the repair path for an external labeled prefix
P/p.
1. A primary edge router PEi SHOULD only choose the edge router PEj
and the repair label rLi as a repair path for the prefix P/p if
label advertised for the prefix P/p by the repair edge router
PEj is allocated on per-VPN or per-CE/per-next-hop basis.
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The reason for this is as follows. As mentioned in the abstract
and Introduction, the core of the network SHOULD remain BGP-free
and the size of the routing table on a core router SHOULD remain
independent of the number of BGP prefixes. BGP prefix grouping
in section 2 ..2.2. requires two prefixes to belong to two
different groups if the labels advertised by the repair PE for
the two prefixes are different. Thus if the repair edge router
allocates labels on per-prefix basis, protected edge router PEi
will advertise a different primary next-hop for each protected
prefix. This is equivalent to having core router "P" knowing
about every BGP prefix. In addition the size of the routing
table of the "P" router becomes comparable to the number of BGP
prefixes.
2. If the repair edge router PEj advertises a repair label as
described in [ .11], then the protected edge router PEi MAY choose
the repair label advertised by PEj as the repair label for the
prefix P/p.
Using the repair label specified in [ .11] has two advantages:
o A repairing edge router PEj need not change the primary
label allocation policy (which may be per-prefix) but can be
chosen as repair PE if the repair labels are allocated on
per-CE or per-VRF basis.
o As mentioned in [ .11], an edge router does NOT repair a
packet arriving with a repair label. Hence using the repair
label when re-tunneling the packet towards PEj guarantees
loop freedome in case of PE-CE link failure.
2.4. Forwarding Plane Operation
This section specifies the forwarding plane operation on the core
router "P" when it detects that the protected edge router PEi is no
longer reachable. We assume that the core router has pre-programmed
its forwarding plane according to Sections 2 ..1. and . 2.2. .
2.4.1. For unlabeled prefix
The forwarding table for the route Ri is programmed according to
section . 2.1.4. As soon as the "P" router detects that the primary
next-hop for Ri is not reachable it does the following for any
packet destined to the protected edge router PEi.
1. Decapsulate tunnel header of the arriving packet
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2. Tunnel the packet towards the repair egress PE identified by the
repair next-hop rNHj
2.4.2. For Labeled prefix
The forwarding table for the route Ri is programmed according to
section . 2.2. . Remember that packets tunneled to the egress edge
PEi have a label under the tunnel encapsulation. As soon as the "P"
router detects that the primary next-hop for Ri is not reachable it
does the following for any arriving packet destined to the
protected edge router PEi
1. Decapsulate the tunnel header to expose the labeled packet
2. Swap the label on the top of the packet (irrespective of the
value of that label) with the repair label rLi
3. Tunnel the packet towards the repair egress PE identified by
rNHj
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3. Example
We will use and LDP core as an example. Consider the diagram
depicted in Figure 2 below. We assume that the PEs advertise repair
labels as specified in [ .11]
+-----------------------------------+
| |
| LDP Core |
| |
| PE1
| |\
| | \
| | \
| | \
| | CE1....... VPN prefix
| | / (10.0.0.0/8)
| | / (11.0.0.0/8)
| | /
| |/
PEx P--------PE0 Lo1 = 1.1.1.1/32
| |\ Lo2 = 2.2.2.2/32
| | \
| | \
| | \
| | CE2....... VPN prefix
| | / (20.0.0.0/8)
| | / (21.0.0.0/8)
| | /
| |/
| PE2
| |
| |
+-----------------------------------+
Figure 2 : Edge node BGP FRR in LDP core
1. As we can see, PE0 has 4 prefixes: 10.0.0.0/8, 11.0.0.0/8,
20.0.0.0/8, and 21.0.0.0/8. PE0 may assign a separate label to
each prefix. The method and policy of assigning primary labels
to each prefixes is irrelevant.
2. PE1 advertises the repair label rL1 for prefixes 10.0.0.0/8 and
11.0.0.0/8
3. PE2 advertises the repair label rL2 for prefixes 20.0.0.0/8 and
21.0.0.0/8
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4. As such, PE0 divides its prefixes into two groups
G1 = {10.0.0.0/8, 11.0.0.0/8}
G2 = {20.0.0.0/8, 21.0.0.0/8}
5. When advertising the next-hop to its IBGP peer, PE0 advertises
1.1.1.1 as the next-hop for prefixes belonging to group G1 and
2.2.2.2 as the next-hop for prefixes belonging to group G2.
6. PE0 advertises the prefixes 1.1.1.1/32 and 2.2.2.2/32 using the
usual IGP mechanism.
7. When advertising 1.1.1.1/32 into the core, PE0 advertises rL1
and PE1 as a repair path. When advertising 2.2.2.2/32 into the
core, PE0 advertises rL2 and PE2 as a repair path. The mechanism
by which a repair path is advertised is beyond the scope of the
proposal.
8. On the penultimate hop router "P", LDP assigns a different LDP
label to 1.1.1.1/32 and 2.2.2.2/32. Core routers other than
penultimate hop routers may employ some sort of label
aggregation to reduce the number of LDP labels
9. Assume that the penultimate hop router "P" assigns the local LDP
label L1 for prefix 1.1.1.1/32 and L2 for prefix 2.2.2.2/32
10.On the penultimate router P, the forwarding entry for L1 will be
as follows
Primary path:
- nexthop is PE0.
- swap the incoming outer label with the LDP label towards
1.1.1.1
Repair path
- Pop the incoming LDP label
- Swap the internal label with the repair label rL1
- Push the LDP label towards PE1
- Forward the packet
11.On the core router P, the forwarding entry for L2 will be as
follows
Primary path: Same as L1
Repair Path
- Pop the incoming LDP label
- Swap the internal label with the repair label rL2
- Push the LDP label towards PE2
- Forward the packet
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12.If the P router detects that PE0 is no longer reachable, it can
use the repair path already pre-programmed in the forwarding
plane as described above. Because the repair path is pre-
programmed as in the case of TE and IP FRR, the P router can re-
route traffic very fast
4. Security Considerations
No additional security risk is introduced by using the mechanisms
proposed in this document
5. IANA Considerations
No requirements for IANA
6. Conclusions
This document proposes a method that allows fast re-route
protection against edge node failure or complete disconnected from
the core in a BGP-free core
7. References
7.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[2] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol
4 (BGP-4), RFC 4271, January 2006
[3] Bates, T., Chandra, R., Katz, D., and Rekhter Y.,
"Multiprotocol Extensions for BGP", RFC 4760, January 2007
7.2. Informative References
[4] Marques,P., Fernando, R., Chen, E, Mohapatra, P.,
"Advertisement of the best external route in BGP", draft-
ietf-idr-best-external-02.txt, April 2004.
[5] Wu, J., Cui, Y., Metz, C., and E. Rosen, "Softwire Mesh
Framework", RFC 5565, June 2009.
[6] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[7] De Clercq, J. , Ooms, D., Prevost, S., Le Faucheur, F.,
Connecting IPv6 Islands over IPv4 MPLS Using IPv6 Provider
Edge Routers (6PE)", RFC 4798, February 2007
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[8] Atlas, A. and A. Zinin, "Basic Specification for IP Fast
Reroute: Loop-Free Alternates", RFC 5286, September 2008.
[9] Shand, S., and Bryant, S., "IP Fast Reroute", RFC5714,
January 2010
[10] Shand, M. and S. Bryant, "A Framework for Loop-Free
Convergence", RFC 5715, January 2010.
[11] Bashandy, P., Pithawala, B., and Hietz J., "Scalable, Loop-
Free BGP FRR using Repair Label, "draft-bashandy-idr-bgp-
repair-label-02.txt", June 2011
8. Acknowledgments
Special thanks to Keyur Patel, Robert Raszuk, and Eric Rosen for
the valuable comments
This document was prepared using 2-Word-v2.0.template.dot.
Authors' Addresses
Ahmed Bashandy
Cisco Systems
170 West Tasman Dr, San Jose, CA 95134
Email: bashandy@cisco.com
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