how to shutdown an E1 link when crc received. Automatically

[ranairfan]

we have a configured ppp multilink interfaces between pairs of Cisco 7609 and Cisco 3640a routers and put 15 E1 lines in each of them. Now the problem is whenever any one of the E1 line generates CRC errors it generates delays on the multilink hence as a result of it our Home location servers at both end un sync. We cant afford that. We want that troubling E1 lines to be shutdown automatically so that it does not disturb entire Multilink

[dgahm]

http://www.cisco.com/en/US/products/sw/iosswrel/ps1824/products_configuration_guide_chapter09186a008008009a.html#xtocid16434

Enable Link Quality Monitoring (LQM)

Link Quality Monitoring (LQM) is available on all serial interfaces running PPP. LQM will monitor the link quality, and if the quality drops below a configured percentage, the router shuts down the link. The percentages are calculated for both the incoming and outgoing directions. The outgoing quality is calculated by comparing the total number of packets and bytes sent with the total number of packets and bytes received by the destination node. The incoming quality is calculated by comparing the total number of packets and bytes received with the total number of packets and bytes sent by the destination peer.

When LQM is enabled, Link Quality Reports (LQRs) are sent every keepalive period. LQRs are sent in place of keepalives. All incoming keepalives are responded to properly. If LQM is not configured, keepalives are sent every keepalive period and all incoming LQRs are responded to with an LQR.

LQR is specified in RFC 1333, "PPP Link Quality Monitoring," by William A. Simpson of Computer Systems Consulting Services.

To enable LQM on the interface, perform the following task in interface configuration mode:

Task Command

Enable LQM on the interface. ppp quality percentage

The percentage argument specifies the link quality threshold. That percentage must be maintained, or the link is deemed to be of poor quality and taken down.

Please rate helpful posts.

[oj88]

A follow-up...

Should I apply this command on all physical ppp interfaces on both routers participating in the MLP bundle?

[vijayasankar]

Hi,

As the LQR reports needs to be exchanged between the Peers in order to measure the quality of the link, LQM should be enabled at both end of the link.

However LQM is not compatible with multilink PPP bundle.

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a00804f2079.html#wp1001080

You can enable LQM only on individual PPP links.

-VJ

[oj88]

One final question:

Cisco mentions a "time lag" so that the link won't bounce up and down. Would somebody know how long is this time lag?

I've looked at RFC 1333 but still can't find any specific info regarding this.

[jackyoung]

There is such indication in the RFC :

Link-Quality-Report packets provide a mechanism to determine the link quality, but it is up to each implementation to decide when the link is usable. It is recommended that this policy implement some amount of hysteresis so that the link does not bounce up and down. A particularly good policy is to use a K out of N algorithm. In such an algorithm, there must be K successes out of the last N periods for the link to be considered of good quality.

What I believe we have to test it to determine the time tag (if you can count it) or let Cisco engineering to tell.

Moreover, the RFC 1989 replaced the 1333.

Hope this helps.

[oj88]

Thank you.