Why internal EIGRP flapping when a WAN link is flapping?

[gwhuang5398]

I have router A and B running EIGRP in between. Router B has a WAN connection into the carrier.

Recently the EIGRP neighboring between A and B was flapping. In the mean time the WAN link was flapping too.

Router B was running BGP over the WAN link and redistributing BGP into EIGRP.

Why the WAN link issue caused the EIGRP neighboring up and down?

Thanks

Gary

[wdrootz]

When we attempted to ping the ISP's router will a full size MTU packet, the packet gets dropped. Any packets greater than 400 bytes gets dropped.