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New Member

SDLC will not recover automatically in the event of link failure

Hi, I've the following scenario in our environment.

ATM device -> modem -> modem -> 3700 router -> <FRAME_RELAY> -> 7600 core_router -> 6500 core_switch -> 3700_SDLC_Router --> IBM AS/400

We've over 20 sites, but the weird things is, most of the sites run just fine, only a few of them having the problem as describe below:

i. If the FR link failed, and ISDN backup does not come up fast enough, the dlsw is ok, but the sdlc connection is not automatically up by itself, it requires some manual intervention over at AS/400 site (sort of like vary on/off)...

ii. Sometimes the dlsw circuits doesn't stay connected for long, may be less than 1 minutes then it dissapears...and re-appear and dissapear...

What's the main course of the flapping circuit and sdlc connection? Anything I could do to provide more detail information? Customer is sceptical in allowing us to do the debugging of sdlc an datalink switching, as they've a bad experience whereby the debug cause the halt of the main SDLC router and causes lots of issues...

Anything I could perform to gather more information instead of debugging? I wish to gather enough information and perhaps open a TAC case later on.

In the mean while, I've attach some configuration of our devices and would appreciate if you guys could go through it and see whether everything is ok...

I tried to compared the IOS version, the configuration line-by-line, everything seems ok, but only there's few branches having this problem..and to top it off, it happens intermittently...

hope to seek some helps over here, thanks

New Member

Re: SDLC will not recover automatically in the event of link fai

I've found the following statement from one of the thread in Netpro forum:

1. the same vmac cannot assign to two SDLC interfaces on the same router

Looking at the serial2/0 and serial2/1 (Remote Router) in the attached txt file, am I hitting the violation of doing that?

Cisco Employee

Re: SDLC will not recover automatically in the event of link fai


Generally speaking it's not a good idea to not

have the same SDLC VMAC under multiple

interfaces, but the actual VMAC is formed by

the left most 5 bytes of the VMAC with the

SDLC polling address appended to the end. For

example, for your remote branch router

attachment config, Serial2/0 would have a VMAC

of 4000.2222.8160 and Serial2/1 would have a

VMAC of 4000.2222.81F0. So they are different

and thus OK.

Now, on to the problem...

The first thing to do when the circuit to an

ATM drops and does not recover is to do a

sho interface serial x/y. Please include that

output in your reply. It should have a line

in it like:

sdlc addr xx state is

That, along with all the other information

is going to tell us which side needs to do

what to bring up the connection.

You should also do:

sho dlsw peer

sho dlsw reach

sho dlsw circuit detail

Once we get that we'll have more information

as to how to pursue.

Here's a good link to DLSw SDLC



Ed Mazurek