[c-nsp] IOS XR - advertising additional paths with RR

Thu Aug 22 18:26:39 EDT 2013

Hi,

I'm trying to lab out a setup for core PIC on IOS XR using 4.2.3. I'm
not sure if my understanding of the feature is correct, so please
correct me if I'm going down the rabbit hole.

My setup:

PE1---P1/RR--PE2
     \      |        /
           P2

(both PE1 and PE2 are multihomed to P1/RR and P2, there is a link
between P1/RR and P2)

PE1 - ASR901 (15.3.3) (lo0: 10.122.129.255)
PE2 - ASR903 (3.10.0) (lo0: 10.123.129.2)
P1 - ASR9k (4.2.3) (lo0: 10.123.129.1)
P2 - ME3600x (3.10.0) (lo0: 10.123.129.3)

PE1 is part of the 'access' domain (unified MPLS) and has BGP sessions
with both P1/RR and P2. PE2 is part of the 'core' domain and only has
a session with P1/RR
P2 is part of the 'core' domain and has a session with P1/RR (and PE1
for the 'access')

P1/RR is the core RR for P2 and PE2.
P1/RR is access RR for PE1
P2 is access RR for PE1.

I expect that if I enable core PIC for ipv4 I should be able to see
both paths from PE2 to PE1 (i.e via P1/RR and P2) on P2. And
conversely I should be able to see both  paths from PE1 to PE2.

on PE1 I can see both paths to PE2 (10.123.129.2):

#sh ip bgp 10.123.129.2
BGP routing table entry for 10.123.129.2/32, version 106
Paths: (2 available, best #1, table default)
  Additional-path-install
  Not advertised to any peer
  Refresh Epoch 1
  Local
    10.123.129.11 (metric 2) from 10.123.129.11 (10.123.129.1)
      Origin IGP, metric 0, localpref 100, valid, internal, best
      Community: 17492:1100 17492:62902
      Originator: 10.123.129.2, Cluster list: 10.123.129.1
      mpls labels in/out nolabel/16012
      rx pathid: 0x1, tx pathid: 0x0
  Refresh Epoch 2
  Local
    10.123.129.14 (metric 2) from 10.123.129.14 (10.123.129.3)
      Origin IGP, metric 0, localpref 100, valid, internal, backup/repair
      Community: 17492:1100 17492:62902
      Originator: 10.123.129.2, Cluster list: 10.123.129.3, 10.123.129.1
      mpls labels in/out nolabel/43
      rx pathid: 0, tx pathid: 0

#sh ip cef 10.123.129.2
10.123.129.2/32
  nexthop 10.122.129.1 Vlan4001 label [implicit-null|26] 16012
    repair: attached-nexthop 10.122.129.9 Vlan4002

That works because there are two distinct BGP sessions (with P1/RR and P2).

However on PE2 I can only see one path for PE1 (10.122.129.255):

#sh ip bgp 10.122.129.255
BGP routing table entry for 10.122.129.255/32, version 59
Paths: (1 available, best #1, table default)
  Additional-path-install
  Not advertised to any peer
  Refresh Epoch 1
  Local
    10.123.129.1 (metric 10) from 10.123.129.1 (10.123.129.1)
      Origin IGP, metric 0, localpref 100, valid, internal, best
      Community: 17492:1100 17492:40129 17492:62911
      Originator: 10.122.129.255, Cluster list: 10.123.129.1
      mpls labels in/out nolabel/16013
      rx pathid: 0, tx pathid: 0x0

That can be traced back to the P1/RR setup, that can see both paths to
PE1 (direct and via P2):

#sh bgp ipv4 u 10.122.129.255
Fri Aug 23 10:06:47.813 NZST
BGP routing table entry for 10.122.129.255/32
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                 66          66
    Local Label: 16013
Last Modified: Aug 23 09:46:28.961 for 00:20:18
Paths: (2 available, best #1)
  Advertised to peers (in unique update groups):
    10.123.129.3    10.123.129.2
  Path #1: Received by speaker 0
  Advertised to peers (in unique update groups):
    10.123.129.3    10.123.129.2
  Local, (Received from a RR-client)
    10.122.129.255 (metric 2) from 10.122.129.255 (10.122.129.255)
      Received Label 3
      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best
      Received Path ID 0, Local Path ID 1, version 66
      Community: 17492:1100 17492:40129 17492:62911
  Path #2: Received by speaker 0
  Not advertised to any peer
  Local, (Received from a RR-client)
    10.123.129.3 (metric 10) from 10.123.129.3 (10.122.129.255)
      Received Label 40
      Origin IGP, metric 0, localpref 100, valid, internal, backup, add-path
      Received Path ID 0, Local Path ID 2, version 66
      Community: 17492:1100 17492:40129 17492:62911
      Originator: 10.122.129.255, Cluster list: 10.123.129.3

The second path is seen as the 'backup' correctly, but doesn't get
advertised to anyone.

The BGP setup on P1/RR looks like this:

router bgp 17492
 nsr
 bgp router-id 10.123.129.1
 bgp graceful-restart
 ibgp policy out enforce-modifications
 address-family ipv4 unicast
  additional-paths receive
  additional-paths send
  additional-paths selection route-policy RP-ADDITIONAL-PATH-TO-BGP
  network 10.123.129.1/32 route-policy RP-LOOPBACK-TO-BGP
  allocate-label all

 neighbor-group VC-RR
  remote-as 17492
  dscp cs6
  password encrypted 01050549590C16
  update-source Loopback0
  address-family ipv4 labeled-unicast
   route-policy RP-BGP-ADJUST-NHOP out
  !
  address-family vpnv4 unicast
  !
  address-family vpnv6 unicast
  !
  address-family l2vpn vpls-vpws
  !

 neighbor-group VC-RR-CLIENT
  use neighbor-group VC-RR
  address-family ipv4 labeled-unicast
   route-reflector-client
  !
  address-family vpnv4 unicast
   route-reflector-client
  !
  address-family vpnv6 unicast
   route-reflector-client
  !
  address-family l2vpn vpls-vpws
   route-reflector-client

neighbor-group VC-ACCESS
  remote-as 17492
  dscp cs6
  password encrypted 01050549590C16
  update-source Loopback10
  address-family ipv4 labeled-unicast
   route-reflector-client
   next-hop-self
  !
  address-family vpnv4 unicast
   route-reflector-client
  !
  address-family vpnv6 unicast
   route-reflector-client
  !
  address-family l2vpn vpls-vpws
   route-reflector-client
  !
 !
 neighbor 10.122.129.255
  use neighbor-group VC-ACCESS
  description PE1
 !
 neighbor 10.123.129.2
  use neighbor-group VC-RR-CLIENT
  description PE2

route-policy RP-ADDITIONAL-PATH-TO-BGP
  set path-selection backup 1 advertise install
end-policy

So how should I setup the ASR9k to advertise the backup paths to all
it's clients?
I found this presentation (h
ttp://www.cisco.com/web/SK/expo2012/pdf/advanced_routing_resilliency_josef_ungerman_cisco.pdf
) that mentions that 'solution C' - add path (page 48) is available in
XR 4, but the config presented only shows IOS setup. I tried to
tab-through the options on the 9k, but there doesn't seem to be
anything there on the neighbour level.

kind regards
Pshem