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An NE40E and an NE80E Selected Different BGP Routes Due to Version Feature Changes

Publication Date:  2013-10-29 Views:  13 Downloads:  0
Issue Description

Network topology:

 

Fault symptoms:

The NE5000E and T1600 were BGP reflectors and reflected the 27.158.140.0/22 network segment advertised by router 2xx.x.33.130. However, the NE40E and NE80E selected different routes.

The routing information on the NE80E is as follows:

<NE80E>disp bgp routing-table

Total Number of Routes: 1620

BGP Local router ID is 2xx.x.33.219
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete

Network NextHop MED LocPrf PrefVal Path/Ogn

*>i 27.158.140.0/22 2xx.x.33.130 0 100 0 ?
*>i                                2xx.x.33.130 0 100 0 ?

 

The routing information on the NE80E is as follows:

<NE40E>disp bgp routing-table

Total Number of Routes: 1620

BGP Local router ID is 2xx.x.33.242
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete

Network NextHop MED LocPrf PrefVal Path/Ogn

*>i 27.158.140.0/22 2xx.x.33.130 0 100 0 ?
* i                                 2xx.x.33.130 0 100 0 ?

Specifically, the NE40E selected only one route, whereas the NE80E selected both the routes.

 

Version information:

NE80E: V300R006C01SPC003
NE40E: V600R001C00SPC800
Handling Process

To address the issue, Huawei performed the following operations and observed the following information:

1. Checked the NE40E's BGP configurations.

The configured number of equal-cost BGP routes was not 1.

2. Checked the BGP routes configured on both the NE80E and NE40E.

Information about BGP routes configured on the NE80E is as follows:

disp bgp routing-table 27.158.140.0

bgp local router id : 2xx.x.33.219
local as number : 64727
paths: 2 available, 2 best
bgp routing table entry information of 27.158.140.0/22:
from: 2xx.x.33.8 (2xx.x.33.8)
relay nexthop: 2xx.x.31.182
original nexthop: 2xx.x.33.130
convergence priority: 0
as-path nil, origin incomplete, med 0, localpref 100, pref-val 0, valid, internal, best, pre 200
originator: 2xx.x.33.146
cluster list: 2xx.x.33.8
not advertised to any peer yet

bgp routing table entry information of 27.158.140.0/22:
from: 2xx.x.33.7 (2xx.x.33.7)
relay nexthop: 2xx.x.31.182
original nexthop: 2xx.x.33.130
convergence priority: 0
as-path nil, origin incomplete, med 0, localpref 100, pref-val 0, valid, internal, best, pre 200
originator: 2xx.x.33.146
cluster list: 2xx.x.33.7
not advertised to any peer yet

 

Information about BGP routes configured on the NE40E is as follows:

disp bgp routing-table 27.158.140.0

bgp local router id : 2xx.x.33.242
local as number : 64727
paths: 2 available, 1 best, 1 select
bgp routing table entry information of 27.158.140.0/22:
from: 2xx.x.33.7 (2xx.x.33.7)
route duration: 37d21h12m12s
relay ip nexthop: 2xx.x.32.62
relay ip out-interface: gigabitethernet1/0/0
original nexthop: 2xx.x.33.130
qos information : 0x0
as-path nil, origin incomplete, med 0, localpref 100, pref-val 0, valid, internal, best, select, active, pre 200
originator: 2xx.x.33.146
cluster list: 2xx.x.33.7
not advertised to any peer yet

bgp routing table entry information of 27.158.140.0/22:
from: 2xx.x.33.8 (2xx.x.33.8)
route duration: 37d21h12m15s
relay ip nexthop: 2xx.x.32.62
relay ip out-interface: gigabitethernet1/0/0
original nexthop: 2xx.x.33.130
qos information : 0x0
as-path nil, origin incomplete, med 0, localpref 100, pref-val 0, valid, internal, pre 200, not preferred for peer address
originator: 2xx.x.33.146
cluster list: 2xx.x.33.8
not advertised to any peer yet
Based on the preceding information, it is known that both the NE80E and NE40E had received routes to network segment 27.158.140.0/22 reflected by the two RRs and the two routes on the NE40E had the same attributes. However, the NE40E selected only one.

3. Consulted with R&D engineers.

It is known that an NE40E/NE80E running a version earlier than V600R001 does not check whether the next hops are the same before forming equal-cost routes, whereas an NE40E/NE80E running V600R001 or later checks and does not form equal-cost routes if the next hops are the same. Therefore, in this case, the two routes reflected by the two RRs were best routes on the NE80E, whereas the NE40E selected only the route received from the peer with a smaller IP address.
Root Cause
An NE40E/NE80E running a version earlier than V600R001 does not check whether the next hops are the same before forming equal-cost routes, whereas an NE40E/NE80E running V600R001 or later checks and does not form equal-cost routes if the next hops are the same.
Solution
None
Suggestions
Product features change with versions, so learn the changes before performing an upgrade.

END