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[Enterprise SONiC] BGP Unnumbered Follow

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kojui_chang 張恪睿
  • Updated

In the original BGP configuration, it needs to specify a peer IPv4 address to establish peer connections.

For CLOS deployment in the data center, the IP interfaces grow dramatically due to the full connection between spines and LEAFs.

(each peer connection needs IPv4 addresses on it). To eliminate this situation, we need the unnumbered interface to establish peer connections.

Restriction

  • "BGP unnumbered" support for Layer 3 interfaces that bind IP on a port or port-channel interface.
  • (202006.x, 202012.x) "BGP unnumbered" support VLAN interface, but it must configure IPv4 address to VLAN interface to activate IPv6 link-local IP address, please make sure there's only one Interface added to the VLAN since BGP session is point to point.
    • The reason why VLAN interface needs extra IP address to be configured is IPv6 link-local address is created automatically on Linux netdevice. If user create 4k VLAN, it will create the 4k corresponding router interface even it doesn't configure any IP address. This will exhaust ASIC resources in this scenario, so we limit IPv6 link-local address to create router interface automatically. In order to make BGP unnumbered work, it indeed needs a router interface on it, so we let user to configure extra IP on it as a workaround
  • The version 202006 and 202012, the Ethernet interface didn't require the additional setting for BGP unnumbered.
  • After version 202111 or later, the Ethernet interface requires the additional setting for BGP unnumbered, "link-local-only" must be enabled first before using BGP unnumbered.
    For example, enable "link-local-only" on Ethernet0. 
    admin@sonic:~$ sudo config interface ipv6 enable use-link-local-only Ethernet0
    admin@sonic:~$ show ipv6 link-local-mode 
    +------------------+----------+
    | Interface Name   | Mode     |
    +==================+==========+
    | Ethernet0        | Enabled   |
    +------------------+----------+
    | Ethernet1        | Disabled |
    +------------------+----------+

Tested model & firmware version:

  • Switch model name:
    DCS203 (AS7362-56X)
    DCS204 (AS7726-32X)
    DCS201,202 (AS5835-54X(T))
  • Edgecore SONiC version:
    202006.4
    202012.0 ~ 202012.4
    202111.0 ~ 202111.3

Establish BGP unnumbered session

mceclip0.png

Procedure:

Step 1. Initialize FRR configuration. Please refer to FRRouting and config initialization tutorial.

Step 2. Enter Vty shell.

admin@sonic:~$ vtysh
Hello, this is FRRouting (version 7.2.1-sonic).
Copyright 1996-2005 Kunihiro Ishiguro, et al.

sonic#

Note.

"vtysh" provides a combined frontend to all FRR daemons in a single combined session.

Step 3. Configuring BGP Neighbor Session with unnumbered. Replaces the IP configuration of the original neighbor with the locally connected interface. (refer to Establish BGP session)

Switch#1's setting.
sonic# configure terminal
sonic(config)# router bgp 65000 
sonic(config-router)#bgp router-id 3.3.3.3 
sonic(config-router)# neighbor Ethernet8 interface remote 65001 

Switch#2's setting.
sonic# configure terminal 
sonic(config)# router bgp 65001 
sonic(config-router)#bgp router-id 4.4.4.4 
sonic(config-router)# neighbor Ethernet48 interface remote 65000

Note.

The AS number of neighbors, you could assign the AS number of neighbors. The "external" is to eBGP and the "internal" is to iBGP. 

eBGP:
sonic(config-router)# neighbor Ethernet8 interface remote-as external
iBGP:
sonic(config-router)# neighbor Ethernet8 interface remote-as internal

 

Step 4. Checking the BGP connection and neighbor status.

On the AS7726-32X (Switch1)

sonic# show bgp summary 

IPv4 Unicast Summary:
BGP router identifier 3.3.3.3, local AS number 65000 vrf-id 0
BGP table version 0
RIB entries 0, using 0 bytes of memory
Peers 1, using 727 KiB of memory

Neighbor        V         AS   MsgRcvd   MsgSent   TblVer  InQ OutQ  Up/Down State/PfxRcd   PfxSnt Desc
Ethernet8      4      65001         3         3        0    0    0 00:00:14            0        0 N/A

Total number of neighbors 1

sonic# show bgp neighbors 
BGP neighbor on Ethernet8: fe80::36ef:b6ff:fe95:2000, remote AS 65001, local AS 65000, external link
Hostname: sonic
 BGP version 4, remote router ID 4.4.4.4, local router ID 3.3.3.3
  BGP state = Established, up for 00:00:27
  Last read 00:00:26, Last write 00:00:26
  Hold time is 180, keepalive interval is 60 seconds
  Neighbor capabilities:
    4 Byte AS: advertised and received
    Extended Message: advertised and received
    AddPath:
      IPv4 Unicast: RX advertised IPv4 Unicast and received
    Extended nexthop: advertised and received
      Address families by peer:
                   IPv4 Unicast
    Route refresh: advertised and received(old & new)
    Enhanced Route Refresh: advertised and received
    Address Family IPv4 Unicast: advertised and received
    Hostname Capability: advertised (name: sonic,domain name: n/a) received (name: sonic,domain name: n/a)
    Graceful Restart Capability: advertised and received
      Remote Restart timer is 120 seconds
      Address families by peer:
        none
  Graceful restart information:
    End-of-RIB send: IPv4 Unicast
    End-of-RIB received: IPv4 Unicast
    Local GR Mode: Helper*
    Remote GR Mode: Helper
    R bit: True
    Timers:
      Configured Restart Time(sec): 120
      Received Restart Time(sec): 120
    IPv4 Unicast:
      F bit: False
      End-of-RIB sent: Yes
      End-of-RIB sent after update: Yes
      End-of-RIB received: Yes
      Timers:
        Configured Stale Path Time(sec): 360
  Message statistics:
    Inq depth is 0
    Outq depth is 0
                         Sent       Rcvd
    Opens:                  1          1
    Notifications:          0          0
    Updates:                1          1
    Keepalives:             1          1
    Route Refresh:          0          0
    Capability:             0          0
    Total:                  3          3
  Minimum time between advertisement runs is 0 seconds

 For address family: IPv4 Unicast
  Update group 1, subgroup 1
  Packet Queue length 0
  Community attribute sent to this neighbor(all)
  0 accepted prefixes

  Connections established 1; dropped 0
  Last reset 00:00:43,  No AFI/SAFI activated for peer
Local host: fe80::6f8:f8ff:fe6a:f691, Local port: 179
Foreign host: fe80::36ef:b6ff:fe95:2000, Foreign port: 41428
Nexthop: 3.3.3.3
Nexthop global: fe80::6f8:f8ff:fe6a:f691
Nexthop local: fe80::6f8:f8ff:fe6a:f691
BGP connection: shared network
BGP Connect Retry Timer in Seconds: 120
Read thread: on  Write thread: on  FD used: 30

On the AS5835-54X  (Switch2)

sonic# show bgp summary 

IPv4 Unicast Summary:
BGP router identifier 4.4.4.4, local AS number 65001 vrf-id 0
BGP table version 0
RIB entries 0, using 0 bytes of memory
Peers 1, using 727 KiB of memory

Neighbor        V         AS   MsgRcvd   MsgSent   TblVer  InQ OutQ  Up/Down State/PfxRcd   PfxSnt Desc
Ethernet48      4      65000         3         3        0    0    0 00:00:21            0        0 N/A

Total number of neighbors 1

sonic# show bgp neighbors 
BGP neighbor on Ethernet48: fe80::6f8:f8ff:fe6a:f691, remote AS 65000, local AS 65001, external link
Hostname: sonic
  BGP version 4, remote router ID 3.3.3.3, local router ID 4.4.4.4
  BGP state = Established, up for 00:00:35
  Last read 00:00:34, Last write 00:00:34
  Hold time is 180, keepalive interval is 60 seconds
  Neighbor capabilities:
    4 Byte AS: advertised and received
    Extended Message: advertised and received
    AddPath:
      IPv4 Unicast: RX advertised IPv4 Unicast and received
    Extended nexthop: advertised and received
      Address families by peer:
                   IPv4 Unicast
    Route refresh: advertised and received(old & new)
    Enhanced Route Refresh: advertised and received
    Address Family IPv4 Unicast: advertised and received
    Hostname Capability: advertised (name: sonic,domain name: n/a) received (name: sonic,domain name: n/a)
    Graceful Restart Capability: advertised and received
      Remote Restart timer is 120 seconds
      Address families by peer:
        none
  Graceful restart information:
    End-of-RIB send: IPv4 Unicast
    End-of-RIB received: IPv4 Unicast
    Local GR Mode: Helper*
    Remote GR Mode: Helper
    R bit: True
    Timers:
      Configured Restart Time(sec): 120
      Received Restart Time(sec): 120
    IPv4 Unicast:
      F bit: False
      End-of-RIB sent: Yes
      End-of-RIB sent after update: Yes
      End-of-RIB received: Yes
      Timers:
        Configured Stale Path Time(sec): 360
  Message statistics:
    Inq depth is 0
    Outq depth is 0
                         Sent       Rcvd
    Opens:                  1          1
    Notifications:          0          0
    Updates:                1          1
    Keepalives:             1          1
    Route Refresh:          0          0
    Capability:             0          0
    Total:                  3          3
  Minimum time between advertisement runs is 0 seconds

 For address family: IPv4 Unicast
  Update group 1, subgroup 1
  Packet Queue length 0
  Community attribute sent to this neighbor(all)
  0 accepted prefixes

  Connections established 1; dropped 0
  Last reset 00:00:35,  Waiting for peer OPEN
Local host: fe80::36ef:b6ff:fe95:2000, Local port: 41428
Foreign host: fe80::6f8:f8ff:fe6a:f691, Foreign port: 179
Nexthop: 4.4.4.4
Nexthop global: fe80::36ef:b6ff:fe95:2000
Nexthop local: fe80::36ef:b6ff:fe95:2000
BGP connection: shared network
BGP Connect Retry Timer in Seconds: 120
Read thread: on  Write thread: on  FD used: 30

 

 Step 5. Save the routing setting.

sonic# write

Note: this version of vtysh never writes vtysh.conf
Building Configuration...
Integrated configuration saved to /etc/frr/frr.conf
[OK]

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