cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
824
Views
5
Helpful
5
Replies

vlan & ttl problem

ccrespoh
Level 1
Level 1

Hello,

I've configured three vlan's over a catalyst 6509 series. My terminal is in the vlan1 and I'm comparing the differents ttl when I send an icmp echo request to machines of vlan2 and vlan3.

When I send an icmp to vlan2 machine (always from the vlan1) I get a TTL of 63. When I do the same to a vlan3 machine, the TTL is 254.

I don't know which could be the problem. The configuration of both vlan's (2 & 3) are the same. The ip route command show me two entries and both of them are directly connected. There's no other devices in the path. All the machines are plugged directly to the Catalyst.

Any idea about that isue?

Thanks in advance.

5 Replies 5

milan.kulik
Level 10
Level 10

Hi,

are the target machines running the same OS?

I noticed I receive ttl=255 when I do ping to a Solaris machine and ttl=128 when I do ping to a Windows machine (both in the same VLAN as my PC).

Regards,

Milan

Hi,

Oops, I've never noticed it, and it's true. I've tried to ping from inside VLAN3 and I get a TTL=64.. From the VLAN1 was 63, so it seems to be "normal".

I'm looking for the reason that explain why the connection between vlan's is a bit slow and when I saw the TTL I thought it could be the reason.. but now I know I look for more.

Thanks

Solaris = 255ttl

Windows = 128ttl

Linux = 64ttl

Milan,

I'm missing something here. This must be the TTL on the response, right? Does the TTL on the outgoing ping also vary in the same way according to the OS of the ping source? I notice that the ping response from an IOS router has TTL=255.

Kevin Dorrell

Luxembourg

Yes, exactly.

Pinging from a Linux PC to a Windows one:

ttl=64 in the echo request and ttl=128 in the echo reply.

That's why traceroute is more comfortable if you want to know the number of hops between the source and destination.

Regards,

Milan