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Wan protocols


"The routers should be using the CISCO default layer 2 WAN protocol" 

Which protocol is the default layer 2 WAN? 

Now I am a bit puzzled. Does the above statement means I should use a default route between routers with known ip addresses? 

I actually established connectivity by configuring PPP encapsulation on all 3 routers. And they are now able to communicate. However I am now second guessing myself. Should I have set a default route instead? Would this meet the requirements of using default layer 2 WAN protocol? 

1 Accepted Solution
8 Replies 8

Hi thanks for the link. But isn't PPP a WAN protocol as well? 

Peter Paluch
Hall of Fame Cisco Employee Hall of Fame Cisco Employee
Hall of Fame Cisco Employee


My friends, please allow me to join.

Luca, I believe that the assignment should be read like this: "Use the WAN protocol that the Cisco routers default to" - or in other words, "Leave the whatever WAN protocol on the interface unchanged" : D

And indeed, @pman is correct - on Cisco IOS-based routers, WAN interfaces such as serial interfaces or Dialer interfaces use HDLC as the encapsulation. Serial interfaces offer many WAN encapsulations - HDLC, PPP, Frame Relay to name the most prominent. And yes, by all means, PPP is a WAN protocol too, and much better than HDLC. But that would be for another debate ; )

Pardon me for stealing the discussion a little.

Best regards,

Hello Peter

Thanks for joining the discussion. 

So can we say it's acceptable that I have configured PPP on 1 router given the other 2 routers where configured with PPP? Now connectivity is restored. 

Many thanks for your help. 






Peter Paluch
Hall of Fame Cisco Employee Hall of Fame Cisco Employee
Hall of Fame Cisco Employee

Hi Luca,

Well, according to the task, PPP is not a correct solution because it is not the default WAN encapsulation on Cisco routers. HDLC is. So if you want to solve your assignment strictly according to the task requirements, you need to use HDLC instead. You can revert to it using "encapsulation hdlc" on the WAN interfaces where you used PPP previously. The change needs to be done on both ends of the link.

Keep the questions coming!

Best regards,

Hi Peter thanks so much for the clarification. It makes sense. I'll definitely change the encapsulation to HDLC. 

Thanks so much for your support. 



Martin L
VIP Advisor VIP Advisor
VIP Advisor

Based on the statement, you should use HDLC, not PPP.  HDLC is only Cisco default protocol for all serial interfaces; No need for any special command by default;  you can remove your encapsulation ppp command and run

show interface serial xyz

to see encapsulation type.  PPP is supported by Cisco and it is much better as WAN protocol because supports authentication/authorization among other features.

Regards, ML
**Please Rate All Helpful Responses **

Hi Martin. 

Thanks for that. 

So connectivity will be equally restored by re moving encapsulation on all routers given HDLC would be the default protocol right? 

One other thing please as I really want to make sense of it all. I know this is not what the assignment requires and that I'm probably mixing things up, but I would like to ask if a static route with next hop address would work in this scenario given the devices are directly connected and IP addresses are known? 

Many thanks in advance. 


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