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Community Member

PIC Edge Unipath on A9K 4.0.1

Hello A9K Experts,

I pretend to implement a PIC Edge Unipath solution but it's no working properly on my lab scenario.

The router learns the following prefix from iBGP (MPLS VPN neighbour 10.181.1.7) and from eBGP (195.9.60.1):

* i40.40.40.40/32         10.181.1.7               0    100             0 1234 i

*>                              195.9.60.1               0                      0 1234 i

Only the best entry enters the routing table, as it should:

B    40.40.40.40/32 [20/0] via 195.9.60.1, 00:25:10

I have this configuration for the vrf

router bgp xxxxx

vrf TESTE123

  rd xxxxx:xxxxxxx

  label-allocation-mode per-vrf

  address-family ipv4 unicast

   table-policy Botnet

   additional-paths receive

   additional-paths send

   additional-paths selection route-policy TESTE123

route-policy TESTE123

  pass

end-policy

But cef doesn't take into account the PIC Edge configuration, since only the best path is computed there through the eBGP neighbour.

RP/0/RSP0/CPU0:A9k-03#show cef vrf TESTE123 40.40.40.40/32 detail

Mon Jan  2 12:03:53.786 WET

40.40.40.40/32, version 15, internal 0x40000001 (ptr 0x9cfdc21c) [1], 0x0 (0x0), 0x0 (0x0)

Updated Jan  2 11:37:41.672

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

  gateway array (0x9ccee3c0) reference count 15, flags 0x80600, source rib (3),

                [1 type 3 flags 0x901101 (0x9cd8307c) ext 0x0 (0x0)]

  LW-LDI[type=0, refc=0, ptr=0x0, sh-ldi=0x0]

  Level 1 - Load distribution: 0

  [0] via 195.9.60.1, recursive

   via 195.9.60.1, 5 dependencies, recursive, bgp-ext [flags 0x20]

    path-idx 0

   next hop 195.9.60.1 via 195.9.60.0/30

    Load distribution: 0 (refcount 1)

    Hash  OK  Interface                 Address

    0     Y   GigabitEthernet0/1/0/4.60 remote    

Should the PIC EDGE operation pre-compute the label for the iBGP Path ? Or am i seeing this the wrong way ?

PIC EDGE Multipath with eiBGP multipath works perfectly!

Thanks!

David

1 ACCEPTED SOLUTION

Accepted Solutions
Highlighted
Cisco Employee

Re: PIC Edge Unipath on A9K 4.0.1

Hello David,

Configure the router policy like this

!

route-policy TESTE123

  set path-selection backup 1 install multipath-protect advertise

end-policy

!

Regards,

/A

5 REPLIES
Highlighted
Cisco Employee

Re: PIC Edge Unipath on A9K 4.0.1

Hello David,

Configure the router policy like this

!

route-policy TESTE123

  set path-selection backup 1 install multipath-protect advertise

end-policy

!

Regards,

/A

Community Member

Re: PIC Edge Unipath on A9K 4.0.1

Thanks Akiritch !

It does work! But a few more comments:

The control-plane verification is identical with the PIC Edge Multipath (with eiBGP multipath enabled)

B    40.40.40.40/32 [20/0] via 10.181.1.7 (nexthop in vrf default), 00:01:01

                             [20/0] via 195.9.60.1, 00:01:01

But the forwarding-plane has it´s difference and it works perfectly has intended! Can i assume this is the normal operation ?

RP/0/RSP0/CPU0:A9k-03#show cef vrf TESTE123 40.40.40.40  

Tue Jan  3 10:27:33.188 WET

40.40.40.40/32, version 19, internal 0x40040001 (ptr 0x9cfdc7cc) [1], 0x0 (0x0), 0x4100 (0x9e511368)

Updated Jan  3 10:12:16.365

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

   via 10.181.1.7, 7 dependencies, recursive, backup [flags 0x110]

    path-idx 0

    next hop VRF - 'default', table - 0xe0000000

    next hop 10.181.1.7 via 16009/0/21

     next hop 10.181.64.17/32 Te0/0/0/0.2  labels imposed {16001 16001}

   via 195.9.60.1, 7 dependencies, recursive, bgp-ext [flags 0x20]

    path-idx 1

    next hop 195.9.60.1 via 195.9.60.0/30

     next hop 195.9.60.2/32 Gi0/1/0/4.60 labels imposed {None}

My last questions are:

Why is this feature so poorly documented on the IOSXR command reference and configuration guide ?

How can a Customer Technical Team configure this feature without Cisco Engineers help ?

Or am i looking on the wrong documents ?

Once again thank you!

Cisco Employee

PIC Edge Unipath on A9K 4.0.1

Hello David,

Try “show bgp vrf TESTE123 40.40.40.40”, one path should be marked as the best and another as the backup.

Yes, you are correct, the feature documentation is poor and we have provided this feedback to the documentation team.

Regards,

/A

Community Member

PIC Edge Unipath on A9K 4.0.1

Thanks Akiritch. We did check the bgp table too and the only difference on it between the Multipath and Unipath option  is this:

Multipath

    10.181.1.7 (metric 200) from 10.181.1.7 (10.181.1.7)

      Received Label 16001

      Origin IGP, metric 0, localpref 100, valid, internal, multipath, backup, add-path, import-candidate, imported

     195.9.60.1 from 195.9.60.1 (195.10.10.4)

       Origin IGP, metric 0, localpref 100, valid, external, best, group-best, multipath, import-candidate

Unipath

    10.181.1.7 (metric 200) from 10.181.1.7 (10.181.1.7)

      Received Label 16001

      Origin IGP, metric 0, localpref 100, valid, internal, backup, add-path, import-candidate, imported

    195.9.60.1 from 195.9.60.1 (195.10.10.4)

      Origin IGP, metric 0, localpref 100, valid, external, best, group-best, import-candidate

And the same routing table entry for both

B    40.40.40.40/32 [20/0] via 10.181.1.7 (nexthop in vrf default), 00:03:19

                             [20/0] via 195.9.60.1, 00:03:19

Interesting to note that admin distance of 20 via 10.181.1.7 when it is an iBGP neighbor. It seems necessary to achieve the intended result. And it works!

Once again thank you.

PS: I cannot stress more the fact that the IOSXR documentation is indeed very poor.

Community Member

Re: PIC Edge Unipath on A9K 4.0.1

Hi Experts

 

I followed this discussion to create the BGP PIC. However, after e-BGP link failure, new forwarding path was calculated and put into VRF table instead of using the backup. As per site topology, the first backup would be preferred path. Please see output below. Can you advise?

 

Before e-BGP link down

Routing entry for 10.31.5.128/29
  Known via "bgp 64513", distance 20, metric 0
  Tag 65042
  Number of pic paths 1 , type internal and external
  Installed Jan 14 19:32:02.735 for 15:02:59
  Routing Descriptor Blocks
    10.32.28.74, from 10.32.28.74, BGP external
      Nexthop in Vrf: "default", Table: "default", IPv4 Unicast, Table Id: 0xe0000000
      Route metric is 0
      Label: 0xa3e (2622)
      Tunnel ID: None
      Binding Label: None
      Extended communities count: 0
      Source RD attributes: 0x0000:65042:100
      NHID:0x0(Ref:0)
    10.100.4.100, from 10.100.4.100, BGP backup path
      Nexthop in Vrf: "default", Table: "default", IPv4 Unicast, Table Id: 0xe0000000
      Route metric is 0
      Label: 0x5dd0 (24016)
      Tunnel ID: None
      Binding Label: None
      Extended communities count: 0
      Source RD attributes: 0x0000:65042:100
      NHID:0x0(Ref:0)



After e-BGP link down


Routing entry for 10.31.5.128/29
  Known via "bgp 64513", distance 200, metric 0
  Tag 65042
  Number of pic paths 1 , type internal
  Installed Jan 15 10:35:02.764 for 00:00:03
  Routing Descriptor Blocks
    10.100.1.100, from 10.100.1.100
      Nexthop in Vrf: "default", Table: "default", IPv4 Unicast, Table Id: 0xe0000000
      Route metric is 0
      Label: 0x5e06 (24070)
      Tunnel ID: None
      Binding Label: None
      Extended communities count: 0
      Source RD attributes: 0x0000:65042:100
      NHID:0x0(Ref:0)
    10.100.4.100, from 10.100.4.100, BGP backup path
      Nexthop in Vrf: "default", Table: "default", IPv4 Unicast, Table Id: 0xe0000000
      Route metric is 0
      Label: 0x5dd0 (24016)
      Tunnel ID: None
      Binding Label: None
      Extended communities count: 0
      Source RD attributes: 0x0000:65042:100
      NHID:0x0(Ref:0)

 


"route-policy BGP_PIC
  #***Fast Failover in BGP***
  set path-selection backup 1 install multipath-protect advertise
end-policy
!"

"router bgp 64513
 bgp router-id 10.100.3.100
 bgp graceful-restart
 bgp log neighbor changes detail
 address-family vpnv4 unicast
  additional-paths receive
  additional-paths send
  additional-paths selection route-policy BGP_PIC
  retain route-target all"

 

 

Regards,

Sumanta.

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