Reset Search
 

 

Article

BGP fast external failover doesn't work if BGP peer doesn't advertise any routes

« Go Back

Information

 
TitleBGP fast external failover doesn't work if BGP peer doesn't advertise any routes
Symptoms
eBGP fast external failover doesn't work:
* X670V-48x[lab].66 # show bgp  
Enabled             : Yes               OperStatus          : Up
RouterId            : 10.0.0.3          AS                  : 65000
LocalPref           : 100               MED                 : None
Always-Compare-MED  : Disabled          Aggregation         : Disabled
Route Reflector     : No                RR ClusterId        : 0
IGP Synchronization : Disabled          New Community Format: Disabled 
Routes from EBGP    : 0                 Routes from IBGP    : 0
Routes redistributed: 0                 Out Updates queued  : 0
Fast Ext Fallover   : Enabled           MPLS LSP as Next-Hop: No
AS Disp Format      : Asplain           Maximum ECMP Paths  : 1
Adj-RIB-Out Storage : Disabled
ConfedId            : 0       
Confed Peers        : 
Networks            : 0
Aggregate Networks  : 0
Redistribute        :
Advertise Inactive Routes: 
 ipv4-unicast   : Disabled 
 ipv4-multicast : Disabled 
 ipv6-unicast   : Disabled 
 ipv6-multicast : Disabled
* X670V-48x[lab].67 # show bgp neighbor 10.34.34.4 transmitted-routes all
Advertised Routes:
     Destination                         Next-Hop        LPref Weight MED        AS-Path
----------------------------------------------------------------------------------------
 
Flags: (*) Preferred BGP route, (>) Active, (d) Suppressed, (h) History
       (s) Stale, (m) Multipath, (u) Unfeasible

* X670V-48x[lab].68 # show sharing 
Load Sharing Monitor
Config    Current Agg     Min    Ld Share  Flags Ld Share  Agg Link  Link Up
Master    Master  Control Active Algorithm       Group     Mbr State Transitions
================================================================================
    25     25     LACP       1    L2        A     25        Y     A       5
                                  L2              26        Y     A       4
================================================================================
Link State: A-Active, D-Disabled, R-Ready, NP-Port not present, L-Loopback
Minimum Active: (<) Group is down. # active links less than configured minimum
Load Sharing Algorithm: (L2) Layer 2 address based, (L3) Layer 3 address based
                        (L3_L4) Layer 3 address and Layer 4 port based
                        (custom) User-selected address-based configuration
Custom Algorithm Configuration: ipv4 L3-and-L4, xor
Distribution Mode Flags:
       A - All: Distribute to all members
       L - Local Slot: Distribute to members local to ingress slot
       P - Port Lists: Distribute to per-slot configurable subset of members
Number of load sharing trunks: 1
* X670V-48x[lab].69 # show bgp neighbor 
 
     Peer            AS         Weight State        InMsgs OutMsgs(InQ)  Up/Down
-----------------------------------------------------------------------------------
Ee-- 10.34.34.4      65001      1      ESTABLISHED  28     32    (0    ) 0:0:10:54
 
Flags: (d) disabled, (e) enabled, (E) external peer, (I) internal peer
       (m) EBGP multihop, (r) route reflector client
 
BGP Peer Statistics
  Total Peers       : 1
  EBGP Peers        : 1                 IBGP Peers          : 0
  RR Client         : 0                 EBGP Multihop       : 0
  Enabled           : 1                 Disabled            : 0

[simulate link fail]

* X670V-48x[lab].70 # show sharing 
Load Sharing Monitor
Config    Current Agg     Min    Ld Share  Flags Ld Share  Agg Link  Link Up
Master    Master  Control Active Algorithm       Group     Mbr State Transitions
================================================================================
    25            LACP       1    L2        A     25        -     R       5
                                  L2              26        -     R       4
================================================================================
Link State: A-Active, D-Disabled, R-Ready, NP-Port not present, L-Loopback
Minimum Active: (<) Group is down. # active links less than configured minimum
Load Sharing Algorithm: (L2) Layer 2 address based, (L3) Layer 3 address based
                        (L3_L4) Layer 3 address and Layer 4 port based
                        (custom) User-selected address-based configuration
Custom Algorithm Configuration: ipv4 L3-and-L4, xor
Distribution Mode Flags:
       A - All: Distribute to all members
       L - Local Slot: Distribute to members local to ingress slot
       P - Port Lists: Distribute to per-slot configurable subset of members
Number of load sharing trunks: 1
* X670V-48x[lab].71 # show bgp neighbor 
 
     Peer            AS         Weight State        InMsgs OutMsgs(InQ)  Up/Down
-----------------------------------------------------------------------------------
Ee-- 10.34.34.4      65001      1      ESTABLISHED  28     33    (0    ) 0:0:11:35
 
Flags: (d) disabled, (e) enabled, (E) external peer, (I) internal peer
       (m) EBGP multihop, (r) route reflector client
 
BGP Peer Statistics
  Total Peers       : 1
  EBGP Peers        : 1                 IBGP Peers          : 0
  RR Client         : 0                 EBGP Multihop       : 0
  Enabled           : 1                 Disabled            : 0
* X670V-48x[lab].72 # show log 
01/25/2017 16:28:15.75 <Noti:BGP.NeighborMgr.PeerEstTrans> [VR 0x00000002] Peer 10.34.34.4 (0) has entered or left Established state, EST? 0, holdtime: 180, passive: 0
01/25/2017 16:26:09.21 <Info:LACP.RemPortFromAggr> Remove port 26 from aggregator
01/25/2017 16:26:09.21 <Info:vlan.dbg.info> Port 26 is Down, remove from aggregator 25
01/25/2017 16:26:09.21 <Info:vlan.msgs.portLinkStateDown> Port 26 link down - Local fault
01/25/2017 16:26:02.69 <Info:vlan.dbg.info> Port 25 is Down, remove from aggregator 25
01/25/2017 16:26:02.69 <Info:LACP.RemPortFromAggr> Remove port 25 from aggregator
01/25/2017 16:26:02.69 <Info:vlan.msgs.portLinkStateDown> Port 25 link down - Local fault
 
A total of 7 log messages were displayed.
Environment
  • EXOS 15.x, 16.x, 21.x
  • All EXOS platforms
  • BGP
Cause
eBGP fast external failover will not happen if eBGP peer doesn't advertise any routes. BGP session will be torn down after holddown timer expires.
Resolution
Observed behaviour is expected and is by design: the purpose of failover is to action changes to the network quickly when a BGP neighbour fails. Before the UPDATEs are exchanged, there are no changes to the network, so failover is not necessary.

As a workaround BFD for BGP can be used:
* X460G2-48t-10G4[lab].66 # show bgp neighbor 
 
     Peer            AS         Weight State        InMsgs OutMsgs(InQ)  Up/Down
-----------------------------------------------------------------------------------
Ee-- 10.10.10.8      65008      1      ESTABLISHED  19     22    (0    ) 0:0:00:37
 
Flags: (d) disabled, (e) enabled, (E) external peer, (I) internal peer
       (m) EBGP multihop, (r) route reflector client
 
BGP Peer Statistics
  Total Peers       : 1
  EBGP Peers        : 1                 IBGP Peers          : 0
  RR Client         : 0                 EBGP Multihop       : 0
  Enabled           : 1                 Disabled            : 0
* X460G2-48t-10G4[lab].67 # show bgp neighbor 10.10.10.8 received-routes all 
 
Routes:
     Destination         Peer            Next-Hop        LPref Weight MED        AS-Path
----------------------------------------------------------------------------------------
 
Flags: (*) Preferred BGP route, (>) Active, (d) Suppressed, (h) History
       (s) Stale, (m) Multipath, (u) Unfeasible
 
Origin: (?) Incomplete, (e) EGP, (i) IGP
 
BGP Route Statistics 
  Total Rxed Routes : 0
  Feasible Routes   : 0
  Active Routes     : 0
  Rejected Routes   : 0
  Unfeasible Routes : 0
 
* X460G2-48t-10G4[lab].68 # disable ports 49
* X460G2-48t-10G4[lab].69
* X460G2-48t-10G4[lab].69 # show log
02/20/2017 15:31:01.66 <Noti:BGP.NeighborMgr.PeerEstTrans> [VR 0x00000002] Peer 10.10.10.8 (0) has entered or left Established state, EST? 0, holdtime: 180, passive: 0
02/20/2017 15:30:59.45 <Info:vlan.msgs.portLinkStateDown> Port 49 link down
 
A total of 2 log messages were displayed.
* X460G2-48t-10G4[lab].70 # show configuration "bgp" 
#
# Module bgp configuration.
#
configure bgp AS-number 65005
configure bgp routerid 10.0.0.5
enable bgp fast-external-fallover
create bgp neighbor 10.10.10.8 remote-AS-number 65008
configure bgp neighbor 10.10.10.8 bfd on
enable bgp neighbor 10.10.10.8
enable bgp
* X460G2-48t-10G4[lab].71 #
Additional notes
Fast-external-failover requirements will be changed when CR: xos0067488 will be implemented. Mentioned CR will force BGP session tear down when corresponding port goes down.
BGP fast external failover doesn't work when received EBGP route NH is not same as peer IP

Feedback

 

Was this article helpful?


   

Feedback

Please tell us how we can make this article more useful.

Characters Remaining: 255