Symptom
This was seen in an MSO environment where leafs had tunnels down to the dci-ucast TEP pointing to remote spines.
On the spine directly connected to that leaf, in the BGP->ISIS redistribution route-map we saw two BGP entries. One for BGP "bgp-425000203" and the other for "bgp--44965293" with the latter being the issue.
Furthermore, the negative AS value was present in the BGP database. Because of this ISIS was sending a notification from the negative BGP AS number instead of the expected one and causing the dci-ucast TEP to not be installed into ISIS DB and the leaf tunnels going down.
Conditions
-Route-maps show negative values
-BGP database might show negative AS values
-Leaf tunnels relying on redistribution route-maps from BGP->ISIS will be down
-Fault will be seen in GUI for those leaf tunnels down
Workaround
Use a BGP AS number of 0-2147483647
