[c-nsp] MTU woes with tunnels

[Justin M. Streiner]

On Fri, 16 Mar 2007, Mattias Eliasson wrote:

> We have a problem where all MTU settings where working before reboot of
> the hub.
> Now (after reboot) some sites are unreachable from windows clients and
> I cant seem to resolve the issue.

Have you tried adding "ip tcp adjust-mss XXX" to your tunnels?

jms

> All equipment is cisco except the NAT router who is a linksys (though
> one end point is PIX and has the same issue).
> Changing the MTU on the NATs does nothing.
>
> Toppology is something like this:
>
> 6503/Sup32 ----------[ tunnel0 ]----------  1801 ----- NAT
>      |
> |
>      ------------------------[tunnel1]--------------
>
> Where tunnel0 is over our net and tunnel1 is over the internet for
> fallback.
>
>
> *********************************************************
>
> HUB conf
>
> interface Loopback1
>  description FastIP GRE source interface 1
>  ip address xxxxxxxxxxx yyyyyyyyyyyyyy
> !
> interface Loopback2
>  description FastIP GRE source interface 2
>  ip address 8xxxxxxxxxxx yyyyyyyyyyyyyy
> !
> interface Tunnel100
>  description FastIP GRE Primary
>  bandwidth 10000
>  ip address xxxxxxxxxxx yyyyyyyyyyyyyy
>  no ip redirects
>  ip mtu 1472
>  ip nhrp map multicast dynamic
>  ip nhrp network-id 100
>  ip nhrp holdtime 300
>  no ip mroute-cache
>  ip ospf network broadcast
>  ip ospf cost 10
>  ip ospf mtu-ignore
>  delay 1000
>  tunnel source Loopback1
>  tunnel mode gre multipoint
> !
> interface Tunnel101
>  description FastIP GRE Secondary
>  bandwidth 10000
>  ip address xxxxxxxxxxx yyyyyyyyyyyyyy
>  no ip redirects
>  ip mtu 1472
>  ip nhrp map multicast dynamic
>  ip nhrp network-id 101
>  ip nhrp holdtime 300
>  no ip mroute-cache
>  ip ospf network broadcast
>  ip ospf cost 20
>  ip ospf mtu-ignore
>  delay 1000
>  tunnel source Loopback2
>  tunnel mode gre multipoint
>
>
> *************************************************
> Spoke
>
> interface Tunnel0
>  description GRE Primary
>  ip address xxxxxxxxxxx yyyyyyyyyyyyyy
>  no ip redirects
>  ip mtu 1472
>  ip nhrp map multicast dynamic
>  ip nhrp map xxxxxxxxxxx yyyyyyyyyyyyyy
>  ip nhrp map multicast zzzzzzzzzzzzz
>  ip nhrp network-id 100
>  ip nhrp holdtime 300
>  ip nhrp nhs zzzzzzzzzzzzzzzz
>  ip ospf network broadcast
>  ip ospf cost 10
>  ip ospf mtu-ignore
>  delay 1000
>  tunnel source Vlan2
>  tunnel mode gre multipoint
> !
> interface Tunnel1
>  description GRE Secondary
>  ip address xxxxxxxxxxx yyyyyyyyyyyyyy
>  no ip redirects
>  ip mtu 1472
>  ip nhrp map multicast dynamic
>  ip nhrp map xxxxxxxxxxx yyyyyyyyyyyyyy
>  ip nhrp map multicast zzzzzzzzzzzzz
>  ip nhrp network-id 101
>  ip nhrp holdtime 300
>  ip nhrp nhs zzzzzzzzzzzzz
>  ip ospf network broadcast
>  ip ospf cost 20
>  ip ospf mtu-ignore
>  delay 1000
>  tunnel source BVI1
>  tunnel mode gre multipoint
>
>
>
> Thankfull for any advice.
>
> Mattias Eliasson
> Omnitron
>
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