I have 2x 2811 routers at a remote hub connected to the network core using GRE tunnels & using HSRP for redundancy. I have recently employed EIGRP in the core which extends over the GRE tunnels to the remote hub routers. The remote hub connects to ships using satellite & as the vsat equipment only uses RIP i am redistributing RIP into EIGRP. I am seeing an intermittant routing loop on the active router for the 1800 Cisco router on board the vessels which doesn't seem to affect the vsat modem it is connected to & the loop disappears after a certain period of time. I can get rid of it by adding a /32 static route to the router & if i remove the static route the loop does not return. Only when the vessel drops out the network & comes back in does the loop return. I am using dynamic routing because ships can roam from from one satellite beam to another & therefore one remote hub to another which is supposed to be fully automated but at present i have to add or remove static routes as ships come & go.
The tunnel is mapped to the routers fa0/0 interface & recently i have seen %IP_VFR-4-FRAG_TABLE_OVERFLOW: messages on the routers log. I have increased the value from 16 to 32 then 64 using the "ip virtual-reassembly max-reassemblies" interface command, but this doesn't seem to have made any difference.
The traces i have run show the packets reaching the active router at the remote hub but instead of taking the rip route to the remote vessel it takes the default route out into the internet, back into our core & back out to the remote hub via the GRE tunnel. The Eigrp & RIP routes are being propagated properly so i am not sure why this is happening. We have another remote hub where RIP from the ships is redistributed into EIGRP without any problems & only difference being the link to the core in an E1 not GRE tunnels.