Back to back "routers on a stick"

Have a little trouble with connectivity loss in this scenario;

router1 switch1 switch2 router2

router1 is running dot1q vlan encapsultion.

router2 is also running dot1q vlan enacpasulation.

the ports on switch1 and switch2 that are connected to the routers are dot1q trunk ports.

the ports that are connected via crossover between switch1 and switch2 are vlan access ports.

everything works fine for several days, then locks up. all interfaces show linked and up, but no ip trafic will pass. ressetting switch 2 corrects the problem.

any ideas? bad hardware or bad config?

relevant configs;


'subinterface connected to vlan trunk port on switch1 interface FastEthernet0/0.10 encapsulation dot1Q 10 ip address x.x.x.x no ip redirects no ip unreachables no ip proxy-arp no ip mroute-cache no keepalive no cdp enable


'connected to router1 interface FastEthernet0/1 duplex full speed 100 switchport trunk encapsulation dot1q switchport mode trunk ! 'conected to switch2 interface FastEthernet0/2 duplex full speed 10 switchport access vlan 10


'port coneted to switch1 interface FastEthernet0/9 switchport access vlan 209 switchport mode access switchport protected load-interval 30 duplex full speed 10


interface GigabitEthernet13/2.9 encapsulation dot1Q 209 ip address x.x.x.x no ip directed-broadcast

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Checked for port errors on each device? Could try hard-setting everything to 10/half, or twiddle the nerd-knobs on fa0/9 some.


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Mark Lar


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please see:

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The question was asked on Usenet, doesn't it seem sensible to answer it here as well?

Reply to
Mark Lar

Besides, the answer given is wrong!

Reply to
Mark Lar

This looks like a school question to me:)

Could be bad hardware but there are other things to check first.

Are there port errors. Are port traffic counters incrementing?

Try running say ospf and see if you can maintain a neighbour relationship between the routers. Log neighbour changes. Check the arp tables, you could have a duplicate address Check the CAM tables on the switches. i.e. sh mac-address

if ospf is too frightening or you don't have it hsrp would probably do. Use debug. Make sure logging is enabled.

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