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Knowledge Base

redirect ip-nexthop common problem

Publication Date:  2019-07-27  |   Views:  539  |   Downloads:  3  |   Author:  rahathossain@huawei.com  |   Document ID:  EKB0000381580

Contents

Issue Description

Referring to the attachment, therehas two Uplink. one is BTCL and another is Mango. They have two IP pool, one is xxx.xxx.15.0/24 which is published through Mango and another is 202.128.254.0/24 which is published through BTCL. Thus incoming BGP load balance has been ensured.
but problem is that two link have the unequal bandwidth and
Customer don’t want to import full routing table rather it just import default route only.
Their requirement was that, traffic comes from xxx.xxx.15.0/24 only should go through MANGO link.
That’s why I have created one traffic policy named MANGO (see attachment name PBR_first_solution.txt). in that way customer initial requirement was served.
But at this point customer facing one problem like below(see the topology.ppt)
When PC(xxx.xxx.15.100) try to communicate with mail server(xxx.xxx.15.250)
It can communicate no problem, but traffic is going to mango link  and then come back  to mail server. Customer told that, this should not be happened. They asked me to give them a solution and without changing the  redirect ip-nexthop command.

Alarm Information

NA

Handling Process

To handle this situation I have created one more  traffic classifier and behavior(PBR_final solution) which has the common name bb
in “classifier bb” where I mentioned about ACL 3777. which is below
 acl number 3777                                                               
 rule 5 permit ip source xxx.xxx.15.0. 24 destination xxx.xxx.254.0. 24
 rule 10 permit ip  source xxx.xxx.15.0. 24  destination xxx.xxx.15.0. 24
 
Along with   the classifier bb I have created one traffic behavior “bb” where I permit ACL 3777  traffic  such that NE40E can check the local routing table that is If source traffic is  from xxx.xxx.15.0 network and destination is  local  network that means either xxx.xxx.15.0/24 network or xxx.xxx.254.0/24 network , NE40E will check the local routing table and it will not go to Mango Link.
I have declare the new classifier and behavior bb like the below sequence.
traffic policy mango                                                           
classifier bb behavior bb 
classifier aa behavior aa
interface GigabitEthernet1/0/0                                                 
 description TO_C7200                                                          
 ip address xxx.xxx.254.28 255.255.255.0
traffic policy mango inbound  
so when PC(xxx.xxx.15.100) try to communicate with mail server(xxx.xxx.15.250) at first traffic come to gi 1/0/0 interface where traffic policy  Mango is applied to inbound. Then based on traffic policy Mango ,  first it will check whether the destination  address is belongs to its local network or not with “classifier bb behavior bb”. if it is in local routes it send back the traffic through gi1/0/0 interface and reach to  local destination like mail server(xxx.xxx.15.250) through its local backbone.
If  PC(xxx.xxx.15.100) try to communicate with  remote network like xxx.xxx.34.1 server first it will check “classifier bb behavior bb” and find that destination network is not  local then it checks  “classifier aa behavior aa”  which redirect all traffics to Mango link through “redirect ip-nexthop xxx.xxx.192.1 “command. 
Thus customer requirement is full filled and customer is satisfied with my solution

Root Cause

Actually I  use “ redirect  ip-nexthop xxx.xxx.195.1”  command to redirect the outgoing traffic towards Mango link from the source xxx.xxx.15.0/24 network.
But in our router when we use redirect command it does  not check its local routing table at all, it just forward all traffic to xxx.xxx.195.1 until that interface is physically down.
So in this case when  PC(xxx.xxx.15.100) tried to communicate with mail server(xxx.xxx.15.250) all traffic from PC comes to interface gi1/0/0 ,it just send all traffic to mango link without checking whether the destination is its local network or remote.

Suggestions

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