I had an interesting problem today. The customer has two lines: MPLS and internet with dmvpn running on both.
Suddenly the voice quality dropped, and we saw that the tunnel over MPLS is down.
The route to the DMVPN hub goes through the mpls line with the IP of the CE router being 172.16.0.1
However, the arp entry for 172.16.0.1 was incomplete. Clearly the line was faulty.
A ticket to to the telecom was raised but the answer was unexpected: you haven’t been using the line for the last seven days.
I was like: what do you mean we’re not using the line! we’re not using the line because it’s DOWN, that’s what it is…but i began to think about it: in every answer there’s a grain of truth…
So i pinged the broadcast 172.16.0.255 and VOILA – 172.16.0.2 responded. But what is 172.16.0.2??? Let’s experiment since the line is down anyway
I changed the static route to go through the .2 address and of course the line was working again.
It turned out that the telecom replaced the line a while ago and changed the ip address of the CE router.
Now my point is here: i only used logic and one simple ip route command. No big deal, yet nobody else has come up with the idea to look for other addresses on the subnet. This is great new for beginners in the IT world: keep your mind open, be on the ball and even limited knowledge can bring great results.