[c-nsp] MTU woes with tunnels

[Mattias Eliasson]

Hi all

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.

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