Cisco 1721 & ISDN 2

[LedZepRock]

Hello

I have a Cisco 1721 that excepts 2 modules, we are currently using 1 module for ISDN, this gives me 128 across both line as we use Multilink. Now if I add a second card would Multilink work across both interfaces (bri0 & bri1), giving me an increased speed of 256?? I think not, but would like to know for sure.

Also another quick question if I may...

I have noticed that most ISDN configs show the use of an Interface Dialer1, and you then add a static route pointing at the Dialer1, ie to send all traffic over ISDN.

ip router 0.0.0.0 0.0.0.0 Dialer 1

But Cisco books and the such dont seem to use Dialers they seem to use the this command

username test password stinky
dialer map ip 172.16.2.1 broadcast name Test 021511651654

Why is there 2 methods?? whats the differance?? which one should I use??

Thanks

Simon

 

[eabbink]

multilink wont work over multiple bri interfaces as it's an ISDN interface feature for linking the (2) B-channels of the ISDN line. You may be able to do load-balancing though over multiple interfaces.

dialers, dialer-pools and groups are more flexible than dialer maps.

a dialer is a virtual interface and with the pools and groups you can use many dialers, each with a unique configuration on one or more bri interfaces. Dialers only use a B channel when they need it.

 

[LedZepRock]

OK great, Thanks for the information.

Simon

 

[gaveeve]

According to Cisco eabbink is incorrect about MP only being for ISDN. I seem to recall that you can even combine a serial link with an ISDN.

"Multilink PPP (MP) allows devices to send data over multiple point-to-point data links to the same destination by implementing a named virtual link. The MP connection has a maximum bandwidth equal to the sum of the component links bandwidth. MP can be configured for all interfaces that support the Point-to-Point Protocol (PPP). Refer to RFC 1990 for more information on MP."

 

[eabbink]

yup, that is correct. MPPP should be able to link all kinds of interfaces. I was thinking only of isdn B-channel-bonding .

sorry for the confusion.

 

[LedZepRock]

OK, well I am a tad confused now, I was OK with no

So can I use Multilink across BRI0 & BRI1, I am only interested in ISDN at the moment....

How would that be configured to work???

Simon

 

[gaveeve]

This is a good link showing several configs plus the explanation behind it.

http://www.cisco.com/warp/public/131/mppp-ddr.html

The main thing is to remember with dialers is to put the command ppp multilink on both the actual bri interface and also the dialer.

 

[LedZepRock]

Hey, thanks for the link very useful, hey you are smart guys so..... I have 2 dialers, 1 needs to use NAT so I have put

ip nat outside (on dialer2)
ip address 80.80.80.80 255.255.255.0 (will not except a 255.255.255.255??) (on dialer 2)

ip nat inside (on FastEthernet0)

debug ip nat does seem to show NAT working, but will that have a negetive effect on dialer1, and is there anything else I need to add for NAT.

Ta
Simon