[c-nsp] BGP NHT on 7600 SRC2

[Dan Peachey]

Hi,

I am testing BGP next-hop tracking on SRC2 code release for the 7600. I
have a pretty simple setup as follows:

PE1 ----- P1 ------- 
 |       / |        |
 |     RR1 |       PE3
 |       \ |        |
PE2 ----- P2 ------- 

PE1 and 2 are 7600's running 12.2(18)SXF5. RR1 is a 7204VXR running
12.0(32)S2. PE3 is the 7600 running 12.2(33)SRC2 where I am
concentrating my tests.

I have IS-IS and LDP running between all routers advertising next-hop
loopbacks. All 3 PE's have VPNv4 iBGP sessions to RR1 and are configured
as RR clients. Next-hop tracking is turned off on the RR.

I have a VRF configured on all 3 PE's with different RD's like so:

!
ip vrf convergence-test
 description vrf for convergence testing
 rd 1000:[1-3]
 route-target export 1000:4
 route-target import 1000:4
!

On PE1 and PE2 I have a SVI in the convergence-test VRF with IP's in the
range 192.168.10.0/24 which I am redistributing into BGP (on the back of
both PE's I have a switch in this VLAN with a host hanging off and VRRP
running on the PE's).

Here is the VPNv4 routing table on PE3 for the VRF:

PE3#sh ip bgp vpnv4 vrf convergence-test
BGP table version is 621, local router ID is xx.xxx.128.239
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
Route Distinguisher: 1000:3 (default for vrf convergence-test)
* i192.168.10.0     xx.xxx.128.247           0    100      0 ?
*>i                 xx.xxx.128.246           0    100      0 ?
*> 192.168.11.0/30  0.0.0.0                  0         32768 ?
*>i192.168.16.128/30
                    xx.xxx.128.246           0    100      0 ?

The loopback of PE1 is .246 and PE2 is .247 so you can see that the
preferred next-hop is currently PE1.

Now the problem I have is when I shutdown the loopback of PE1 to remove
it from the IGP, PE3 appears to notice this and runs the BGP next-hop
tracking scanner after the default 5 second wait (I can see this happen
in debugs) but appears to do nothing after that. The route for
192.168.10.0/24 via .246 is not removed from the VPNv4 table and stays
active until the BGP scanner (default 60 seconds) is run and it
withdraws the route (or the RR BGP scanner is run and withdraws the
route via BGP). Once this happens, then the VPNv4 route updates to
192.168.10.0/24 via .247 as it should.

I am expecting to see the VPNv4 route change after the default 5 second
wait for the next-hop scanner but this is not the case.

Does anyone have any ideas or have experienced similar issues to this?

TIA,

Dan
 

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