Bad hope count on cisco switch

[MParashar]

Hi Everyone,

I have observed multiple bad hope count packets in 'show ip traffic' output of cisco switch as below. Counter is incerementing every second from 15-50 to 300-400 packets.

IP statistics:
Rcvd: 2952921712 total, 1860913607 local destination
30 format errors, 6389 checksum errors, 998915728 bad hop count
27589 unknown protocol, 48385215 not a gateway
0 security failures, 0 bad options, 29760464 with options

Bad hope count is approx 33% of overall traffic. upon debugging the errors  through 'debug ip error' i have found the below dispose packet entries:

6m 44s Debugging (7) IP s= x.x.x.x (VlanX), d=224.0.0.251, len 70, dispose ip.hopcount
26m 44s Debugging (7) IP  s= x.x.x.x (VlanX), d=224.0.0.251, len 70, dispose ip.hopcount
26m 44s Debugging (7) IP s= x.x.x.x (VlanX), d=224.0.0.251, len 70, dispose ip.hopcount
26m 44s Debugging (7) IP s= x.x.x.x (VlanX) , d=224.0.0.252, len 64, dispose ip.hopcount
26m 44s Debugging (7) IP s= x.x.x.x (VlanX) , d=224.0.0.252, len 64, dispose ip.hopcount
26m 44s Debugging (7) IP s= x.x.x.x (VlanX), d=224.0.0.251, len 70, dispose ip.hopcount

Both of the addresses are multicast entries. I am not been able to understand whether it's a normal process or i have to worry about it and if it's a problem then why it's dropping and how can i resolve it. Any suggestions.. 

[marce1000]

 - Check this thread : https://community.cisco.com/t5/other-network-architecture-subjects/ip-traffic-bad-hop-counts/td-p/179363

 M.

[MParashar]

hi ,

I did that, but my query is why these requests are dropping. How can i troubleshoot that

[mlund]

The multicast address range 224.0.0.0/24 is used for local link multicast and should not be routed, therefore the ttl should be set to 1 by sending device. So I think this is what is going on here, this is normal behavior.

[MParashar]

Thank you for the response. but this normal behaviour is accumalating 35% of my overall traffic. Do i have to worry or can ignore it.

[mlund · Accepted solution]

This is mDNS, take a look at this link

https://learn.microsoft.com/en-us/previous-versions//bb878128(v=technet.10)?redirectedfrom=MSDN

If you worry about it, see if there is something that can be turned off in the computers that are sendinding this.

[MParashar]

Thank you for sharing the details. It was really helpful. Although I am still not clear about it's impact but i have a better understanding of it now.

[MHM Cisco World]

IP Multicast Troubleshooting Guide - Cisco

this due to TTL=0 
check cisco recommend for bad hop count