ISDN BRI both channels into E1

[ajenks]

I have a number of remote routers (2821's) that are connected to a core router via serial link. This serial link has a BRI interface defined as a "backup interface". The BRI connects to the core router - the core router actually has a PRI as it needs to (potentially) support connections from multiple remote routers (if event of multiple serial links failing). The remote router initiates the call, the core router never initiates the call. This works fine except it is only configure to use a single BRI channel.

I want to be able to use 128K, not 64K in event of serial link fialing, but I have a number of questions/issues relating to this.

1) I've been told that when a BRI interface is defined as a "backup interface" to another interface you can only use a single B-channel. Is this correct ?

2) The examples I have seen of using 2 B-Channels shows an interface "BRI0" and interface "BRI1" in a rotary-group and a "Dialer1" interface tying them together. However, I only have a BRI0/0/0 interface and can't modify BRI0/0/0:1 or BRI0/0/0:2 (the individual B-Channels) - What's going on ?

3) I have also seen advice on the CISCO site, that suggests I just add "ppp multilink" and a "dialer load-threshold value" to the interface on both routers and this is sufficient to bring up the second B-Channel. Is this correct ?

Any help would be greatly appreciated, I have to make a long-distance site visit to test anything.

[jackyoung]

1) As I remember, uou can configure the dialer interface as backup interface. You can double verify it in Cisco web.

2) I believe you cannot specify the channel but you can configure the dialer isdn spid1 or 2 for two channel, please follow below MLPPP link for example.

Another link for 2nd B channel.

http://www.cisco.com/en/US/tech/tk801/tk379/technologies_tech_note09186a0080094b7a.shtml

3) This is correct and should be enough, follow the example in Cisco web can help.

http://www.cisco.com/en/US/tech/tk713/tk507/technologies_tech_note09186a0080112d3b.shtml

Hope this help.

[ilya.varlashkin · Accepted solution]

Hi,

using BRI directly is old style. These days using Dialer is preferred way. Just assign BRI to the same group that is specified on Dialer, add 'ppp multilink' to Dialer and 'dialer load-threshold 1 either'. The you can either specify dialer as backup for your serial link, or you can use floating static routes to bring ISDN link up.

You can't modify individual channels, two B-channels and the D-channel are all configured on BRI0 interface.

Hope this helps.

[madhur_malik · Accepted solution]

1) No its not correct.

2) No you can't configure B channel Interface directly.

3) Simply configure dialer as a backup interface, also put below config in the dialer.

ppp multilink

ppp multilink load-threshold 180 either

this will make the dialer interface to bundle the links and will initiate the multilink at 180/255 load on interface.

This will solve your problem

Regards

Madhur

[Wilson Samuel]

Hi,

If I'm correct, then you actually want to use both the BRI Channels rather than individual channels.

If this is the case, then my friend you are already getting that results i.e. bydefault unless you configure PPP both the channels are used automatically and you needn't do anything.

Secondly, you dont actually require to go a far site to do testing as you can always use a scheduled reload for a safeguard and configure anything, if that configuration breaks your communication, the router would automatically reload at the specified time and you are safe.

Kind Regards,

PS: Please rate if the thread helps.

[ilya.varlashkin]

You actually have to specify pretty low load-threshold else only single channel comes up with light load.