TTL=2?

[ohassairi]

                   Hello

if you capture one RIP packet you will find that TTL in ip header is 2.

can you explain why is it 2 and not 1 for example? or 255.....

thanks

[Alessio Andreoli]

Hi,
Are you sure you are not analysing the hop count? There is any other protocol like BGP with TTL security?

Alessio

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[ohassairi]

hi

i am not speaking about the hop count. i captured one RIPv1 packet in GNS3. and i was surprised that the TTL field in the IP packet is 2.

i cannot find any explanation for that. the destination IP address is 255.255.255.255 and i think routers do not forward broadcast traffic (including RIP) to other routers. so TTL=1 can be explained but 2 !!!!

[blau grana]

maybe this will help a little bit:

https://learningnetwork.cisco.com/thread/40817

[Peter Paluch]

Hi,

Now that's an interesting idea!

I was in talks with Don Slice exactly about this TTL in EIGRP that also sets the TTL to 2. This is what he wrote to me in a private message - I hope he would not mind me making a part of his answer public:

Interestingly enough, the TTL isn't  set by EIGRP but within the IP infrastructure.  We call the ip code  without the IP parameters set and the infra decides what value to use,  which I assume is based on the protocol type, etc.  I've poked around  their code a bit but haven't found where the decision is made on the TTL  value to use.

So the TTL is not even set by EIGRP itself, and I would assume that's the same for RIP.

Best regards,

Peter