Ping with PPP encap and looped!!!!

[hjerbandi]

Hi,

Just curious about this simple problem.

I hv a P-t-P with encap as hdlc, A and B. Let say that i take a loopback from B the remote end. So In this case i see that serial and line is up and (looped) @ A end. Now i will ping my own interface i.e A's IP and will get ping response.

But with ppp as encap, this is not true. when loop is taken, the local end shows as serial up and line down, and when i ping my own interface, i dont see any responce!!!!

Any explanation on this??

thx

hanu

[amit.shrivastava]

On ppp encapsulation u cannot ping the self interface in looped condition. only u will get the following state" serial 0 line protocol down(looped).This is the usual feature of PPP enacpsulation. If u want to test the link in looped condition, u need to change the encapsulation to hdlc and do it.

Rgds

Amit

[ashok_boin]

Hi,

This is due to PPP protocol implementation. It uses magic numbers with which it can find whenever the line looped back, and make line protocol down. It can find out loop when Input and Output magic numbers are same.

Regards...

Ashok.

[hjerbandi]

ashok,

thx for the info, but i would be intrested in knowing the magic no!!... any link/url would be apperciated

thx

hanu

[kkalaycioglu]

Hi,

http://www.cisco.com/en/US/tech/tk801/tk703/technologies_design_guide_chapter09186a00800de9d8.html#xtocid20 link will show you some outputs of "debug ppp negotiation" command. Basically During LCP negotiation both parties send CONFREQ frames and these frames include a random number called magic number. If magic number field of a received CONFREQ frame is the same as the transmitted one then it's decided that the link is looped. For more info:http://www.ietf.org/rfc/rfc1661.txt?number=1661

Regards and happy new year.