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Knowledge Base

Redistributing UNR routes into EBGP on AR3260

Publication Date:  2019-07-22  |   Views:  1930  |   Downloads:  0  |   Author:  m84068533  |   Document ID:  EKB1001127322

Contents

Issue Description

Fault symptom: Customer needed to know how to redistribute into EBGP, the UNR route existing into the router’s routing table.

Version information: V200R007C00SPCb00

Networking overview: Customer needed to provide Internet to the end user devices that don’t support BGP and which were connected to 2 LNS routers in a failover scenario
and therefore he needed to use dynamic routing,

Handling Process

1.      We have checked the configuration regarding the routes redistribution to EBGP, which seemed to be correct and asked customer to provide us the outputs of the following commands for finding out the detailed attributes of the UNR route: <Huawei>display bgp vpnv4 all routing X.X.199.29
<Huawei>display ip routing-table vpn-instance INTERNET X.X.199.29 verbose
From the outputs, we have observed that the UNR route came into the router with the Flag “NoAdv”, which means that this UNR route wouldn’t be further redistributed by the router to any other protocols.
Routing Table : INTERNET
Summary Count : 1
Destination: X.X.199.29/32
Protocol: Unr             
Process ID: 0

Preference: 63                    
Cost: 0

NextHop: X.X.199.29

        Neighbour: 0.0.0.0
State: Active NoAdv           
Age: 00h02m51s

This UNR route was automatically created by the router, when it delivers the IP address attributed by the RADIUS server, towards the end user. 

2. We needed to find out what was generating the attribute of “NoAdv” of the UNR route and asked customer to provide us the output of the following commands: [Huawei]diagnose; [Huawei-diagnose] display rm unr-route.

For this command, customer provided us the following output:

Destination: X.X.199.29/32

InstanceID: 1                    
UnrType: 0x2

Label: 4294967295           
NextHop: X.X.199.29

IfIndex: 0x12                
TunnelId: 0

Metric: 0                       
Slot: 0

Cid: 16777217                 
Tag: 0

Preference:
0                 
BK_Nexthop: 0.0.0.0

BK_Interface: 0x0              
BK_TunnelId: 0

Flag: 0                        
Key: 0x0

EntryID: 0x68650EE8        

NW_EntryId: 0x0
From the output, we could see that the UnrType is 0x2, which means that the UNR route is created by the PPP module.
We explained to our customer that when receiving a route, the router is checking for the code it has received the route with, and if the route has been created by the PPP module, it will have NoAdv flag. Because it comes with the NoAdv flag, the route can’t be redistributed.
Also, we informed the customer that if he still wanted to distribute the route to other devices,it would be better to try to distribute it from the LAC side (from the user), by EBGP.

3.       Customer informed us that his end user devices don’t support BGP and he needs a configuration to provide them Internet and to use dynamic routing, as he has 2 LNS routers for the failover, he couldn’t use static routes. We asked customer for more information about how do the users establish the L2TP tunnels with the 2 LNS routers – randomly or by fixed sequence and how do the 2 LNS routers work – 2 at one time or only one at one time? Customer wanted to redistribute the UNR routes dynamically, having the LNS routers in a failover scenario. But on AR router the UNR routes created by PPP module can’t be redistributed since they have the NoAdv flag.

4.      Our R&D team tested the complete scenario and we provided customer the following steps to follow:

a) configure a black hole route, like, for example: “ip route-static vpn-instance INTERNET X.X.199.29 24 NULL 0”

b) this route will take effect in the vpn-instance routing-table.

c)  import the static route into BGP; BGP will then redistribute the route. 
 

d
) When a packet arrives in the router, the packet will search the for UNR route, since the UNR route is the exact route, with the 32 mask.

Solution

a) Configure a black hole route, like, for example: “ip route-static vpn-instance INTERNET X.X.199.29 24 NULL 0”

b) this route will take effect in the vpn-instance routing-table.

c) import the static route into BGP; BGP will then redistribute the route.

d) When a packet arrives in the router, the packet will search the for UNR route, since the UNR route is the exact route, with the 32 mask.