DF bit in ip header

[sarahr202]

HI every body!

I just want to ask one question. " don't fragment " bit is set or not set by default in ip header?

thanks a lot and have a nice weekend!

[rais · Accepted solution]

Usually its not set. However, some applications would default to setting it.

Thanks.

[lamav · Accepted solution]

Sarah:

RFC 791 makes no mention of the default setting for the DF bit in the flags field of the IP header.

It depends on the application.

[mattkaya56 · Accepted solution]

Here is what I saw

IP header from the host had DF set

IP header in a RIP response from the router

not set.

Thanks

Mat

[lamav]

Matt;

Im sure you're trying to convey a message with that post. What that message is, however, I have no idea! :-)

[mattkaya56]

I was hoping the experts would explain the why and why not.

Apologize for the confusion.

[sarahr202]

Thanks all of you!

if you guys don't mind, i have a more question.

what is default value for ttl in ip header?

Thanks a lot and have a great weekend!

[Richard Burts · Accepted solution]

In my experience there is not a generic default for the TTL. It is application or vendor dependent. I have seen a lot of implementations that start at 255, and quite a few that start at 64, and some start at 128.

HTH

Rick

[lamav · Accepted solution]

The TTL is set to a value by the source that represents the maximum number of hops it wants for the datagram. Each router decrements the value; if it ever reaches zero the datagram is said to have expired and is discarded.

No default. The TTL is set by the application.