[c-nsp] arp & vrf

[Adrian Pirciu]

When an arp packet arrives, I guess the router checks and discards arp 
requests having a source ip already configured on the router. It seems 
logical to do so. I don't know how and if you can bypass this, without 
the static arps.... Nice trick though :)

On Tuesday 16 November 2004 09:10, Sorin CONSTANTINESCU wrote:
> Hi,
>
> I have a GSR running 120-28.S1, with 2 GigabitEthernet LC
> crossconnected via an optical fiber patch. One of the interfaces is
> in the default routing table (Gi4/0), and the other one is in a vrf.
>
> #sh run int gi4/0
> Building configuration...
>
> Current configuration : 120 bytes
> !
> interface GigabitEthernet4/0
>  ip address 10.0.0.1 255.255.255.252
>  no ip directed-broadcast
>  no negotiation auto
> end
>
> #sh run int gi7/0
> Building configuration...
>
> Current configuration : 146 bytes
> !
> interface GigabitEthernet7/0
>  ip vrf forwarding test#4
>  ip address 10.0.0.2 255.255.255.252
>  no ip directed-broadcast
>  no negotiation auto
> end
>
> I tried to ping 10.0.0.2 from the default routing table, but the
> router couldn't learn an ARP entry because the router knew that
> 10.0.0.2 was on the same router.
>
> #debug ip arp shows:
>
> #show log | i 00b0.c285.4a00|0000.0000.0000
> Nov 16 08:51:38: IP ARP: sent req src 10.0.0.1 00b0.c285.4a00,
>                  dst 10.0.0.2 0000.0000.0000 GigabitEthernet4/0
> Nov 16 08:51:38: IP ARP req filtered src 10.0.0.1 00b0.c285.4a00, dst
> 10.0.0.2 0000.0000.0000 it's our address
> Nov 16 08:51:40: IP ARP: sent req src 10.0.0.1 00b0.c285.4a00,
>                  dst 10.0.0.2 0000.0000.0000 GigabitEthernet4/0
> Nov 16 08:51:42: IP ARP: sent req src 10.0.0.1 00b0.c285.4a00,
>                  dst 10.0.0.2 0000.0000.0000 GigabitEthernet4/0
> Nov 16 08:51:42: IP ARP req filtered src 10.0.0.1 00b0.c285.4a00, dst
> 10.0.0.2 0000.0000.0000 it's our address
> Nov 16 08:51:44: IP ARP: sent req src 10.0.0.1 00b0.c285.4a00,
>                  dst 10.0.0.2 0000.0000.0000 GigabitEthernet4/0
> Nov 16 08:51:44: IP ARP req filtered src 10.0.0.1 00b0.c285.4a00, dst
> 10.0.0.2 0000.0000.0000 it's our address
> Nov 16 08:51:46: IP ARP: sent req src 10.0.0.1 00b0.c285.4a00,
>                  dst 10.0.0.2 0000.0000.0000 GigabitEthernet4/0
> Nov 16 08:51:46: IP ARP req filtered src 10.0.0.1 00b0.c285.4a00, dst
> 10.0.0.2 0000.0000.0000 it's our address
>
> The solution was to set static arp entries:
>
> arp 10.0.0.2 00b0.c285.4b80 ARPA
> arp vrf test#4 10.0.0.1 00b0.c285.4a00 ARPA
>
> Is there another way to make traffic pass via the GBICs?
>
> Regards,

-- 
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Adrian Pirciu -- Network Engineer