Friday, December 19, 2008

What will happen if you see your PE loopback in vpnv4 table

May be the next time you will be weird to see your PE loopback address in VPNv4 routing table. The first thought which comes in mind that how my PE loopback can be part of the VPNv4 routing table because this is the table which actually contains the information of all the VRFs. Is your PE is working as VRF? No, not at all then what’s the reason behind this.

Check the given output which I captured from the RR server.
show ip bgp vpnv4 all | i ( is PE loopback address)
*>i10.169.68.0/24 0 100 0 ?
*>i10.235.10.8/30 0 100 0 ?
*>i10.16.190.8/30 0 100 0 ?
*>i10.80.85.128/25 0 100 0 ?
*>i10.80.97.0/26 0 100 0 ?
*>i10.235.24.8/30 0 100 0 ?
*>i10.235.54.8/30 0 100 0 ?
* i10.176.1.40/30 0 100 0 ?
* i10.176.2.0/30 0 100 0 ?
*>i10.179.32.0/26 0 100 0 ?
*>i10.103.66.48/28 0 100 0 ?
*>i10.10.254.197/32 0 100 0 ?

You can see all the routes are getting with next-hop as PE address. But In the last line you can check the loopback entry is coming as VPNv4 route entry. Actually it should not come. Now the next question comes in mind may be loopback is redistributed in BGP, Go and check you will find it is advertised in IGP not in BGP.
After that I logged in PE router i.e. and ran given the command

PE-Router# show ip bgp vpnv4 all
BGP table version is 176194, local router ID is
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: 6x500:100
*> 0 32768 ?
*>i10.235.5.0/30 0 100 0 ?
*>i10.235.5.4/30 0 100 0 ?
*> 0 32768 ?
Route Distinguisher: 6x000:123
*>i0.0.0.0 10 100 0 ?
*>i10.240.5.0/30 10 100 0 ?
Route Distinguisher: 6x500:24
*>i10.235.1.0/24 0 100 0 ?
*>i10.235.1.32/30 0 100 0 ?
Route Distinguisher: 6x500:640*>i0.0.0.0 0 100 0 ?
*>i17.12.13.11/32 0 100 0 ?
Route Distinguisher: 2:6x500:100
*> 0 ?
*>i14.47.255.241/32 0 100 0 ?

In the above output you can see the last route distinguisher which is 2:6x500:100 explicitly showing is locally originate route and automatically it is binding new RD. This RD is something different from others because it is carrying 2 which explicitly states that it is mdt safi or used for your MVPN traffic. After that I checked RD 6x500:100 which is actually binding to a vrf which is using multicasting. Now check there is one more route which is I did the telnet and checked what’s belong to this route. Then I found a weird thing that the same MVPN client was configured on the router and was the loopback address of the router.

By doing the above exercise I came to know two important things
1) From RR we can get total number of MVPN clients running on particular PE.
2) From particular PE we can fetch the information that where that particular MVPN is actually working.

You can do one more thing on RR check the "show ip bgp vpnv4 all" output of that PE where no MVPN is configured. In the output you will not get PE loopback address.

shivlu jain

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