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Error: Illegal Hdlc Serial Type Code 65535

I have tried to connect two 3700 routers together using a back to back serial point to point connection and when I do show interface on both routers i see interface up line protocol down.

both interfaces are on the same subnet

the router with the dce cable connected is providing the clocking

encapsulation is hdlc at both ends

there is no access control list set

keep alive is set on both interfaces

when i do a debug serial interface on both routers, i get the error message:

Illegal hdlc serial type code 65535

and no keeplives are being exchange

I have tried using the cisco online interpreter and the only suggestion it is givin is that the routers are sending packets that contain unrecognized packets. i really dont know what dat means.

I have tried the same serial cable, serial network modules and configurations on other routers and it works so its more like an issue with the routers. The ios on the 3700 is the v12.4

I will really appreciate it if anyone has a solution to this problem

Community Member

Re: Error: Illegal Hdlc Serial Type Code 65535

To aid anyone who wants to assist in troubleshooting this annoying problem, some output from the DCE and DTE routers are attached.

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