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New Member

IOS-XR <-> IOS CSC Inter-AS not working?


Im trying to get CSC Inter-AS working between ios (c1900-universalk9-mz.SPA.151-4.M4.bin) and ios-xr ( asr9000 4.1.0 ) and I'm unable to get it working. The end result is a CE running MPLS to xconnect into a asr9k för h-vpls type setup.

The L2VPN config is verified before by putting the CE into our IGP and everything works. However when wanting to use ebgp it falls apart:

Currently it is configured like this:                  


interface Loopback0

ip address x.x.x.127


interface GigabitEthernet0/0.1549

encapsulation dot1Q 1549

ip address x.x.x.4

mpls bgp forwarding

mpls label protocol ldp

mpls ip

router bgp 64515

bgp router-id x.x.x.127

bgp always-compare-med

bgp log-neighbor-changes

neighbor x.x.x.5 remote-as 34244


address-family ipv4

  network x.x.x.127 mask

  neighbor x.x.x.5 activate

  neighbor x.x.x.5 prefix-list x  in

  neighbor x.x.x.5 prefix-list x out

  neighbor x.x.x.5 send-label



address-family vpnv4



mpls ldp router-id Loopback0 force

on P router:

interface Loopback0

ipv4 address x.x.x.120


router bgp 34244

bgp router-id x.x.x.120

bgp log neighbor changes detail

address-family ipv4 unicast

  redistribute connected route-policy IPV4-CONNECTED-TO-BGP

  redistribute static route-policy IPV4-STATIC-TO-BGP

  allocate-label all

neighbor x.x.x.4

  remote-as 64515

  address-family ipv4 labeled-unicast

   route-policy x in

   route-policy x out



mpls ldp

     router-id loopback0

     interface gi0/1/0/15.1549


and the BGP seems to be working fine:

RP/0/RSP0/CPU0:rtr10.sjo#show bgp nei x.x.x.4
Fri Jul 20 11:30:37.769 METDST

BGP neighbor is x.x.x.4
Remote AS 64515, local AS 34244, external link
Remote router ID x.x.x.127
  BGP state = Established, up for 19:26:04
  Last read 00:00:34, Last read before reset 00:00:00
  Hold time is 180, keepalive interval is 60 seconds
  Configured hold time: 180, keepalive: 60, min acceptable hold time: 3
  Last write 00:00:06, attempted 19, written 19
  Second last write 00:01:06, attempted 19, written 19
  Last write before reset 00:00:00, attempted 0, written 0
  Second last write before reset 00:00:00, attempted 0, written 0
  Last write pulse rcvd  Jul 20 11:30:31.302 last full not set pulse count 2458
  Last write pulse rcvd before reset 00:00:00
  Socket not armed for io, armed for read, armed for write
  Last write thread event before reset 00:00:00, second last 00:00:00
  Last KA expiry before reset 00:00:00, second last 00:00:00
  Last KA error before reset 00:00:00, KA not sent 00:00:00
  Last KA start before reset 00:00:00, second last 00:00:00
  Precedence: internet
  Enforcing first AS is enabled
  Neighbor capabilities:
    Route refresh: advertised and received
    4-byte AS: advertised and received
    Address family IPv4 Labeled-unicast: advertised and received
  Received 1285 messages, 0 notifications, 0 in queue
  Sent 1174 messages, 0 notifications, 0 in queue
  Minimum time between advertisement runs is 30 secs

For Address Family: IPv4 Labeled-unicast
  BGP neighbor version 145723894
  Update group: 0.1 Filter-group: 0.6  No Refresh request being processed
  Extended community attribute sent to this neighbor
  Route refresh request: received 0, sent 1
  Policy for incoming advertisements is

  Policy for outgoing advertisements is   1 accepted prefixes, 1 are bestpaths
  Cumulative no. of prefixes denied: 0.
  Prefix advertised 107, suppressed 0, withdrawn 3
  Maximum prefixes allowed 131072
  Threshold for warning message 75%, restart interval 0 min
  An EoR was not received during read-only mode
  Last ack version 145723894, Last synced ack version 0
  Outstanding version objects: current 0, max 2
  Additional-paths operation: None

  Connections established 1; dropped 0
  Local host: x.x.x.5, Local port: 179
  Foreign host: x.x.x.4, Foreign port: 40925
  Last reset 00:00:00

and all the routes look good etc.

But when I look in CEF:

RP/0/RSP0/CPU0:rtr10.sjo#show cef x.x.x.127/32

Fri Jul 20 11:33:31.282 METDST

x.x.x.127/32, version 18, drop adjacency, internal 0x4004001 (ptr 0xae650834) [1], 0x0 (0xace7ba70), 0x0 (0xadf366c0)

Updated Jul 19 16:24:29.011

Prefix Len 32, traffic index 0, precedence routine (0)

   via x.x.x.4, 0 dependencies, recursive, bgp-ext [flags 0x20]

    path-idx 0


     local label 16131

it does not seem able to resolve? Which is probably the reason it does not work?

Or have I missed any configuration, do anyone have a working ios-xr 4.1.0 ios inter-as setup working and can share the configuration?

Any hint is appreciated!

Everyone's tags (6)
New Member

I have similar problem. Did

I have similar problem. Did you manage to resolve the BGP-LU prefixes received over eBGP session? In my case as well all looks OK (eBGP LU session up, prefixes with labels exchanged, routing table looks OK), with the exception of CEF:


RP/0/0/CPU0:02-ASBR2#show cef detail 
Thu Jul  3 14:48:04.746 UTC, version 393, drop adjacency, internal 0x4004001 0x0 (ptr 0xacba7fa4) [1], 0x0 (0xacba2640), 0x10 (0xacc33754)
 Updated Jul  3 14:14:07.206
 Prefix Len 32, traffic index 0, precedence n/a, priority 4
  gateway array (0xacb63e7c) reference count 18, flags 0xf2, source rib (6), 0 backups
                [7 type 5 flags 0x210101 (0xacc38048) ext 0x0 (0x0)]
  LW-LDI[type=5, refc=3, ptr=0xacba2640, sh-ldi=0xacc38048]
   via, 0 dependencies, recursive, bgp-ext [flags 0x6020]
    path-idx 0 NHID 0x0 [0xacb0ad08 0x0]
     local label 16016 
     labels imposed {16001}

    Load distribution: 0 (refcount 7)

    Hash  OK  Interface                 Address
    0     Y   Unknown                   drop           



Cisco Employee

Generally, Cisco software

Generally, Cisco software requires a /32 route for each next-hop that should be label switched. In the CSC/Inter-AS B/C options, in IOS-XR you must add manually a /32 static route for the peer address of the interconnection in order to create a label for that. IOS creates automatically a /32 connected route when the relevant VPNv4 or labeled BGP session comes up.

Configuring a Static Route to a Peer

Perform this task to configure a static route to an Inter-AS or CSC-CE peer.

When you configure an Inter-AS or CSC peer, BGP allocates a label for a /32 route to that peer and performs a NULL label rewrite. When forwarding a labeled packet to the peer, the router removes the top label from the label stack; however, in such an instance, BGP expects a /32 route to the peer. This task ensures that there is, in fact, a /32 route to the peer.

Please be aware of these facts before performing this task:

•A /32 route is not required to establish BGP peering. A route using a shorter prefix length will also work.

•A shorter prefix length route is not associated with the allocated label; even though the BGP session comes up between the peers, without the static route, forwarding will not work.

Best Regards,


New Member

Yes. Figured out in the mean

Yes. Figured out in the mean time. Thanks a lot.

Cisco Employee

You are very welcome!Best

You are very welcome!

Best Regards,


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