[c-nsp] Mac Address on ATM Subinterfaces | c1712 routing issue

[Marco Eulenfeld]

Hi,

i have s "small" problem with using 2 dsl lines connected to one 1712
where both lines are terminated on the same Router via ATM-Subinterfaces.
The problem is, that the 1712 doesn't route the directly connected Subnets
correctly. As one can see in the output below, the config is plain simple
without anything special. I have tested the setup also without Router1
and used 2 Ethernets in a Linuxbox (with the same MAC) - same result.

Problem:

a) Ping from Router1 Src 1.1.1.2 Dst 1.1.1.1 works.
b) Ping from 1712    Src 1.1.1.1 Dst 1.1.1.2 works.
c) Ping from 1712    Src 1.1.1.5 Dst 1.1.1.6 doesn't work.

If i ping from Router1 Src 1.1.1.6 Dst 1.1.1.5, it will work and
after that, the Ping c) will work also. Unfortunatly Ping b) doesn't
work anymore.
I can repeat this game and use Ping a) again and after doing that,
PIng b) will work again, but Ping c) doesn't work anymore.

Looks like the 1712 doesn't really route first (routing via Vlan 1 or
Vlan 2) and than looks in the ARP table of the "next-hop-vlan" for the
L2 adress of the next hop.
Everything works fine when there are 2 different MACs as next hops.

My first idea was to change the BIA/ MAC of the ATM Subinterface on Router1,
but i haven't found a command to do it :( (Router1 is a 7200VXR NPE-G1 with
12.2(18)S7)
  
Any hints?

Regards,

Marco

#################

Setup:


1712   -----  dsl ----- atm subinterface (RBE)
 |  fa1 / vlan 1                                Router1
 |----------- dsl ----- atm subinterface (RBE)
    fa2 / vlan 2


Cisco 1712 (MPC862P) processor (revision 0x101) with 86577K/11727K bytes of mem.
Processor board ID FOC08251TGQ (606004915), with hardware revision 0000         
MPC862P processor: part number 7, mask 0                                        
1 Ethernet interface                                                            
5 FastEthernet interfaces                                                       
1 ISDN Basic Rate interface                                                     
1 Virtual Private Network (VPN) Module             

Configuration 1712 Version 12.3(11)T3 and 12.2(15)ZL1

[...]
interface FastEthernet1                                                         
 no ip address                                                                  
!                                                                               
interface FastEthernet2                                                         
 switchport access vlan 2                                                       
 no ip address                 

interface Vlan1                                                                 
 ip address 1.1.1.1 255.255.255.252                                             
!                                                                               
interface Vlan2                                                                 
 ip address 1.1.1.5 255.255.255.252                                             

ip route 0.0.0.0 0.0.0.0 1.1.1.2         

[...]

Router#sh ip arp                                                                
Protocol  Address          Age (min)  Hardware Addr   Type   Interface          
Internet  1.1.1.1                 -   0011.9246.2345  ARPA   Vlan1              
Internet  1.1.1.2                71   0050.0454.e152  ARPA   Vlan1              
Internet  1.1.1.5                 -   0011.9246.2345  ARPA   Vlan2              
Internet  1.1.1.6                72   0050.0454.e152  ARPA   Vlan2