09-07-2006 12:37 AM - edited 03-03-2019 01:54 PM
I've gone as far as configuring MLP using two 2048kbps serial links. In my setup, s0/1 and s0/2 are members of Multilink 2. The problem is, s0/2 goes protocol up and down every several seconds to a minute. My understanding of MLP is that the flapping serial link will be removed from the bundle and let the traffic go through the remaining stable link (s0/1 in this case). But in my scenario, even with s0/2's status is protocol down, if I do a sh ppp multilink, I can see that Multilink 2 treats s0/2 as "active". Being so, I get all kinds of things from debug ppp multilink events.
But if I shutdown s0/2, the problem would disapear.
Please see below:
R1 and R2's MLP configs are mirrors of each other. The following pretty much sums up how both of them are configured:
interface Multilink2
ip address x.x.x.x
ppp multilink
ppp multilink group 2
!
interface Serial0/1
bandwidth 2048
no ip address
encapsulation ppp
ppp multilink
ppp multilink group 2
!
interface Serial0/2
bandwidth 2048
no ip address
encapsulation ppp
ppp multilink
ppp multilink group 2
!
==============================
sh inter s0/2
Serial0/2 is up, line protocol is down
Hardware is GT96K Serial
Description: Tiwi-Digitel
MTU 1500 bytes, BW 2048 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation PPP, LCP Open, multilink Open, loopback not set
.
.
==============================
sh ppp multilink
Multilink2, bundle name is BayArea01
Bundle up for 00:02:00, 2/255 load
Receive buffer limit 24384 bytes, frag timeout 1000 ms
0/0 fragments/bytes in reassembly list
395 lost fragments, 2677 reordered
38/51687 discarded fragments/bytes, 0 lost received
0x1B51 received sequence, 0x1E2A sent sequence
Member links: 2 active, 0 inactive (max not set, min not set)
Se0/1, since 00:00:23
Se0/0, since 00:01:58
==============================
debug ppp multilink events
Sep 7 16:09:22 PH: Mu2 MLP: End bit lost, discard reassembled packet
Sep 7 16:09:22 PH: Mu2 MLP: Lost fragment 19A5 (all links out of sequence)
Sep 7 16:09:22 PH: Mu2 MLP: End bit lost, discard reassembled packet
Sep 7 16:09:22 PH: Mu2 MLP: Begin bit lost, discard fragment 19A8
Sep 7 16:09:22 PH: Mu2 MLP: Lost fragment 19AB (all links out of sequence)
Sep 7 16:09:22 PH: Mu2 MLP: Begin bit lost, discard fragment 19AC
Sep 7 16:09:22 PH: Mu2 MLP: Lost fragment 19B1 (all links out of sequence)pp mul
Sep 7 16:09:22 PH: Mu2 MLP: End bit lost, discard reassembled packet
Sep 7 16:09:22 PH: Mu2 MLP: Lost fragment 19B7 (all links out of sequence)
Sep 7 16:09:22 PH: Mu2 MLP: End bit lost, discard reassembled packet
Sep 7 16:09:22 PH: Mu2 MLP: End bit lost, discard reassembled packet
Sep 7 16:09:22 PH: Mu2 MLP: Lost fragment 19BF (all links out of sequence)
Sep 7 16:09:22 PH: Mu2 MLP: Begin bit lost, discard fragment 19C0
Sep 7 16:09:22 PH: Mu2 MLP: Lost fragment 19C3 (all links out of sequence)
Sep 7 16:09:22 PH: Mu2 MLP: Begin bit lost, discard fragment 19C4
Sep 7 16:09:22 PH: Mu2 MLP: Lost fragment 19D3 (all links out of sequence)
Sep 7 16:09:22 PH: Mu2 MLP: End bit lost, discard reassembled packet
Sep 7 16:09:23 PH: Mu2 MLP: Lost fragment 19E9 (all links out of sequence)
Sep 7 16:09:23 PH: Mu2 MLP: End bit lost, discard reassembled packet
Sep 7 16:09:23 PH: Mu2 MLP: Lost fragment 19ED (all links out of sequence)
Sep 7 16:09:23 PH: Mu2 MLP: End bit lost, discard reassembled packet
.
.
(and several of the following)
Sep 7 16:07:33 PH: Se0/1 MLP: cdp packet forwarded to wrong interface
Sep 7 16:07:33 PH: Se0/1 MLP: cdp packet forwarded to wrong interface
Sep 7 16:07:33 PH: Se0/1 MLP: cdp packet forwarded to wrong interface
.
.
Also, if Multilink 2 balks (as it occassionally does), I have to do a clear interface multilink 2 to restore the link.
Any help is highly appreciated.
09-07-2006 12:49 AM
Hi,
The feature that you are insisting is called Link quality monitoring in PPP.
Unfortunately this feature is not supported for multilink bundles.
You can enable LQM only on individual PPP links, to achieve automatic link monitoring.
This will not work with multilink bundles.
Here's the URL
Check out this thread in the forum.
I would suggest you to perform a complete test with the flapping link with the help of the service provider and rectify the problem on this link.
Hope this helps.
-VJ
09-07-2006 01:07 AM
But the thing is, why is Multilink 2 still using s0/2 even if it's protocol down? If I shutdown s0/2, traffic becomes normal after I do a clear interface multilink 2.
Rectifyig this to the provider is SOP. But in the meantime, I want the router to use the good link with minimum or no human intervention. That, I believe is the real purpose of having two redundant links in the first place.
Speaking of LQM, can I configure ppp quality 80 on s0/1 and s0/2, knowing that they're members of Multilink 2?
09-07-2006 01:17 AM
Hi,
If the line protocol goes down, the multilink shouldn't use the failed link. It should be fault tolerant in that perspective. Not sure whether you are encountering any bug in IOS.
You can check on that.
As the LQM is not supported for multilink, you cannot use it currently in the s0/1 and s0/2.
If you are removing multilink and configuring the s0/1 and s0/2 as normal links then you can use the LQM.
-VJ
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