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  • 1.  BGP sessions up while BFD down

     
    Posted 03-01-2016 06:55

    I'm testing some BFD and BGP configurations.

    I've got two QFX10K switches connected directly together and a simple BGP configuration between them.

    I've also got BFD configured under BGP and it all seems good.

     

    One one QFX i then applied a RE filter to deny BFD traffic (UDP) to test what happens when BFD fails. What I see is the BGP sessions is instantly brought down due to BFD going down.. I see these logs:

     

    Mar  1 22:39:02 qfx-test1 bfdd[1458]: BFD Session 10.1.1.0 (IFL 575) state Up -> Down LD/RD(17/18) Up time:00:18:43 Local diag: AdminDown Remote diag: None Reason: Received Upstream Destroy Session.
Mar  1 22:39:02 qfx-test1 bfdd[1458]: BFDD_TRAP_SHOP_STATE_DOWN: local discriminator: 17, new state: down, interface: irb.10, peer addr: 10.1.1.0
Mar  1 22:39:34 qfx-test1 rpd[1453]: BGP_RESET_PENDING_CONNECTION: 10.1.1.0 (Internal AS 10): reseting pending active connection

    So the BGP sessions goes down for about 30 seconds, but then comes back up, even with BFD is still down.  Is that normal behaviour?  I would think that is BFD remains down, BGP should also stay down...  

     

    thanks. 



  • 2.  RE: BGP sessions up while BFD down

    Posted 03-01-2016 11:30

    Luca ,


    When BFD goes DOWN it brings it’s CLIENT DOWN as well , in this case BFD brings DOWN BGP Session.

    Only after Client is UP [ i.e Protocol Session UP ] , BFD can be programmed for Client .

    Behavior you are observing is EXPECTED .

    After BGP is brought DOWN by BFD , Client tries to Come UP again i.e BGP attempts to ESTABLISH SESSION again .

    BGP Comes UP , but BFD cannot transition to UP due to Firewall Filter to Block BFD PDUs.

    SO BGP stays up while BFD is DOWN .

     

    DUT
    =====

    Scenario ==> I have BFD enabled for Multi-hop IBGP .
    ==========================================

    regress@conjuring# run show bgp summary <=== CORE IBGP SESSION
    Mar 02 00:22:55
    Groups: 5 Peers: 5 Down peers: 0
    Table Tot Paths Act Paths Suppressed History Damp State Pending
    bgp.l3vpn.0
    200006 200006 0 0 0 0
    bgp.l3vpn-inet6.0
    200006 200006 0 0 0 0
    bgp.mvpn.0
    3 3 0 0 0 0
    bgp.mvpn-inet6.0
    3 3 0 0 0 0
    Peer AS InPkt OutPkt OutQ Flaps Last Up/Dwn State|#Active/Received/Accepted/Damped...
    10.255.161.107 65000 13549 17567 0 1 1:46:37 Establ
    bgp.l3vpn.0: 200006/200006/200006/0
    bgp.l3vpn-inet6.0: 200006/200006/200006/0
    bgp.mvpn.0: 3/3/3/0
    bgp.mvpn-inet6.0: 3/3/3/0
    vpna.inet.0: 200006/200006/200006/0
    vpna.inet6.0: 200006/200006/200006/0
    vpna.mvpn.0: 3/3/3/0
    vpna.mvpn-inet6.0: 3/3/3/0

     


    regress@conjuring# run show bfd session extensive <=== BFD FOR BGP [ CORE IBGP ]
    Mar 02 00:29:24

    Detect Transmit
    Address State Interface Time Interval Multiplier
    10.255.161.107 Up 0.450 0.150 3
    Client BGP, TX interval 0.150, RX interval 0.150
    Session up time 01:53:06
    Local diagnostic None, remote diagnostic None
    Remote state Up, version 1
    Replicated
    Session type: Multi hop BFD
    Min async interval 0.150, min slow interval 1.000
    Adaptive async TX interval 0.150, RX interval 0.150
    Local min TX interval 0.150, minimum RX interval 0.150, multiplier 3
    Remote min TX interval 0.150, min RX interval 0.150, multiplier 3
    Local discriminator 52, remote discriminator 22
    Echo mode disabled/inactive
    Remote is control-plane independent
    Multi-hop route table 0, local-address 10.255.162.157
    Session ID: 0x0


    Configure Firewall FiIlter to Discard Incoming BFD Packets.
    ===============================================


    regress@conjuring# set firewall family inet filter mbfd_filterv4 term 1 from destination-port 4784
    Mar 02 00:28:20

    {master}[edit]
    regress@conjuring# set firewall family inet filter mbfd_filterv4 term 1 then count mbfd_filter_count
    Mar 02 00:28:36

    {master}[edit]
    regress@conjuring# set firewall family inet filter mbfd_filterv4 term 1 then discard
    Mar 02 00:28:48

    {master}[edit]
    regress@conjuring# set firewall family inet filter mbfd_filterv4 term 2 then accept
    Mar 02 00:28:54

    {master}[edit]
    regress@conjuring# set interfaces ae2 unit 0 family inet filter input mbfd_filterv4
    Mar 02 00:29:19

    {master}[edit]
    regress@conjuring# commit
    Mar 02 00:29:31
    re0:
    configuration check succeeds
    re1:
    commit complete
    re0:
    commit complete

    {master}[edit]
    regress@conjuring#


    Output after enabling Filter to Block BFD Packets
    =======================================


    regress@conjuring# run show bfd session extensive
    Mar 02 00:29:39

    Detect Transmit
    Address State Interface Time Interval Multiplier
    10.255.161.107 AdminDown 0.450 1.000 3 <==== BFD Going DOWN
    Session down time 00:00:03, previous up time 01:53:17
    Local diagnostic CtlExpire, remote diagnostic None
    Remote state Up, version 1
    Replicated
    Session type: Multi hop BFD
    Min async interval 0.150, min slow interval 1.000
    Adaptive async TX interval 0.150, RX interval 0.150
    Local min TX interval 1.000, minimum RX interval 0.150, multiplier 3
    Remote min TX interval 0.150, min RX interval 0.000, multiplier 3
    Local discriminator 52, remote discriminator 0
    Echo mode disabled/inactive, no-absorb, no-refresh
    Remote is control-plane independent
    Multi-hop route table 0, local-address 10.255.162.157
    Session ID: 0x0


    regress@conjuring# run show bgp summary <==== BGP brought DOWN by BFD
    Mar 02 00:29:50
    Groups: 5 Peers: 5 Down peers: 1
    Table Tot Paths Act Paths Suppressed History Damp State Pending
    bgp.l3vpn.0
    0 0 0 0 0 0
    bgp.l3vpn-inet6.0
    0 0 0 0 0 0
    bgp.mvpn.0
    0 0 0 0 0 0
    bgp.mvpn-inet6.0
    0 0 0 0 0 0
    Peer AS InPkt OutPkt OutQ Flaps Last Up/Dwn State|#Active/Received/Accepted/Damped...
    10.255.161.107 65000 13563 17589 0 2 14 Active

    regress@conjuring# run show bgp neighbor 10.255.161.107
    Mar 02 00:29:59
    Peer: 10.255.161.107 AS 65000 Local: 10.255.162.157 AS 65000
    Group: ibgp Routing-Instance: master
    Forwarding routing-instance: master
    Type: Internal State: Active Flags: <>
    Last State: Idle Last Event: Start
    Last Error: None
    Options: <Preference LocalAddress AddressFamily Rib-group Refresh>
    Options: <BfdEnabled>
    Address families configured: inet-vpn-unicast inet6-vpn-unicast inet-mvpn inet6-mvpn
    Local Address: 10.255.162.157 Holdtime: 90 Preference: 170
    Number of flaps: 2
    Last flap event: BfdDown <=== BGP was brought DOWN by BFD

    {master}[edit]
    regress@conjuring#


    regress@conjuring# run show bgp summary <=== CORE IBGP SESSION is UP
    Mar 02 00:43:58
    Groups: 5 Peers: 5 Down peers: 0
    Table Tot Paths Act Paths Suppressed History Damp State Pending
    bgp.l3vpn.0
    200006 200006 0 0 0 0
    bgp.l3vpn-inet6.0
    200006 200006 0 0 0 0
    bgp.mvpn.0
    3 3 0 0 0 0
    bgp.mvpn-inet6.0
    3 3 0 0 0 0
    Peer AS InPkt OutPkt OutQ Flaps Last Up/Dwn State|#Active/Received/Accepted/Damped...
    10.255.161.107 65000 2285 39 0 2 13:50 Establ <=== CORE IBGP SESSION is UP
    bgp.l3vpn.0: 200006/200006/200006/0
    bgp.l3vpn-inet6.0: 200006/200006/200006/0
    bgp.mvpn.0: 3/3/3/0
    bgp.mvpn-inet6.0: 3/3/3/0
    vpna.inet.0: 200006/200006/200006/0
    vpna.inet6.0: 200006/200006/200006/0
    vpna.mvpn.0: 3/3/3/0
    vpna.mvpn-inet6.0: 3/3/3/0

     

    regress@conjuring# run show bfd session extensive
    Mar 02 00:44:01

    Detect Transmit
    Address State Interface Time Interval Multiplier <===== BFD is DOWN as Filter is enabled to Block Incoming BFD Packets. BFD stays Down until Firewall filter is removed.
    10.255.161.107 Down 0.000 2.000 3
    Client BGP, TX interval 0.150, RX interval 0.150
    Local diagnostic None, remote diagnostic None
    Remote state AdminDown, version 1
    Replicated
    Session type: Multi hop BFD
    Min async interval 0.150, min slow interval 2.000
    Adaptive async TX interval 2.000, RX interval 2.000
    Local min TX interval 2.000, minimum RX interval 0.150, multiplier 3
    Remote min TX interval 0.000, min RX interval 0.000, multiplier 0
    Local discriminator 71, remote discriminator 0
    Echo mode disabled/inactive, no-absorb, no-refresh
    Multi-hop route table 0, local-address 10.255.162.157
    Session ID: 0x0

     

     

    Regards,

    Vinod Kumar.