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Testbed Routing Design

This document discusses the BGP routing design in the Testbed.

              +------+
              +  VM  +---------+
              +------+         |
                               |
              +------+         |
              +  VM  +---------+
              +------+         |
+-------+                  +---+---+     
|  PTF  +------------------+  DUT  |
+-------+                  +---+---+
              +------+         |
              +  VM  +---------+
              +------+         |
                               |
              +------+         |
              +  VM  +---------+
              +------+

In this topology, VMs (vEOS) act as the BGP neighbors of the DUT. VMs generate and advertise BGP routes to the DUT. This approach has several issues:

  • Difficult to generate arbitary routes from the vEOS, e.g., write complex route-map and filter to generate the needed routes.
  • Consume lots of memory in the vEOS
  • Rules are specific the NOS. If we plan to switch VM to SONiC, we need to rewrite all the route-maps.
              +------+
    +---------+  VM  +---------+
    |         +------+         |
    |                          |
    |         +------+         |
    +---------+  VM  +---------+
    |         +------+         |
+---+---+                  +---+---+     
|  PTF  |                  |  DUT  |
+---+---+                  +---+---+
    |         +------+         |
    +---------+  VM  +---------+
    |         +------+         |
    |                          |
    |         +------+         |
    +---------+  VM  +---------+
              +------+

The new approach is use VM as a pass-through device. We run exabgp instances on PTF docker, and exabgp advertise the routes to the VM, and VM then re-advertise the routes to DUT. This approach has several advantages

  • VM template becomes much more simplified. Only basic interface, lag, BGP configuration.
  • VM memory consumption is smaller.
  • Exabgp can generate complex routes.
  • Easy to support different NOS as neigbhor devices, for example SONiC VM.

Implementation details:

  • backplane bridge to physically connect ptf docker and vm. bridge the br-b-{{ testbed name }} is created on the host to connect the eos and ptf via backplane network.
br-b-vms6-1             8000.72bb0a6ad08c       no      VM0100-back
                                                        VM0101-back
                                                        VM0102-back
                                                        VM0103-back
                                                        ptf-vms6-1-b
  • eos vm backplane interface. Et5 is created in eos as the backplane interface.
ARISTA01T1#show int status
Port       Name      Status       Vlan     Duplex Speed  Type            Flags Encapsulation
Et1                  connected    in Po1   full   unconf EbraTestPhyPort                    
Et2                  connected    1        full   unconf EbraTestPhyPort                    
Et3                  connected    1        full   unconf EbraTestPhyPort                    
Et4                  connected    1        full   unconf EbraTestPhyPort                    
Et5        backplane connected    routed   full   unconf EbraTestPhyPort                    
Ma0                  connected    routed   full   10G    10/100/1000                        
Po1                  connected    routed   full   unconf N/A
  • ptf backplane interface. backplane interface is created in ptf docker.
root@6884a0fcd031:~# ip addr show backplane
1359: backplane@if1360: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 96:1f:0e:1f:fc:09 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 10.10.246.254/24 scope global backplane
       valid_lft forever preferred_lft forever
    inet6 fc0a::ff/64 scope global 
       valid_lft forever preferred_lft forever
  • eos bgp connection to exabgp. exabgp_v4 and exabgp_v6 (not shown below) is created in eos to connect with exabgp. The bgp connection is iBGP connection.
ARISTA01T1#show ip bgp sum
BGP summary information for VRF default
Router identifier 100.1.0.29, local AS number 64600
Neighbor Status Codes: m - Under maintenance
  Description              Neighbor         V  AS           MsgRcvd   MsgSent  InQ OutQ  Up/Down State   PfxRcd PfxAcc
  65100                    10.0.0.56        4  65100           5081      5080    0    0    1d07h Estab   2      2
  exabgp_v4                10.10.246.254    4  64600           8277      1880    0    0    1d07h Estab   6399   6399
  • exabgp ansible module to control exabgp service in PTF docker. You can use supervisorctl to check the exabgp service status.
    • create, remove, restart exabgp service using supervisord.
    • each exabgp instance listen to a http port for route announce/withdraw
root@6884a0fcd031:~# supervisorctl status
exabgp-ARISTA01T1                RUNNING   pid 118, uptime 2 days, 8:16:45
exabgp-ARISTA01T1-v6             RUNNING   pid 131, uptime 2 days, 8:16:42
exabgp-ARISTA02T1                RUNNING   pid 92, uptime 2 days, 8:16:53
exabgp-ARISTA02T1-v6             RUNNING   pid 105, uptime 2 days, 8:16:49
exabgp-ARISTA03T1                RUNNING   pid 66, uptime 2 days, 8:17:00
exabgp-ARISTA03T1-v6             RUNNING   pid 79, uptime 2 days, 8:16:57
exabgp-ARISTA04T1                RUNNING   pid 40, uptime 2 days, 8:17:07
exabgp-ARISTA04T1-v6             RUNNING   pid 53, uptime 2 days, 8:17:04
ptf_nn_agent                     RUNNING   pid 14, uptime 2 days, 10:35:21
sshd                             RUNNING   pid 13, uptime 2 days, 10:35:21
  • pytest fib fixture to generate routes to exabgp
    • currently support t0, t1, t1-lag, extending to other topology is straighforward
    • fib module generate http request to exabgp instance

Future applications:

  • multi-path relax test. pytest will instruct multiple exabgp instances to advertise same VIP to different T0 VM.
  • add/remove routes test. pytest will control exabgp to advertise/withdraw routes

How to use exabgp module

start an exabgp instance

        ptfhost.exabgp(name=k,
                       state="started", \
                       router_id = 10.0.0.1, \
                       local_ip  = 10.0.0.1, \
                       peer_ip   = 10.0.0.2, \
                       local_asn = 65100, \
                       peer_asn  = 65100, \
                       port = 6000)

use a fib fixture. The fixture will detect your testbed type and then generate routes based your testbed type.

import pytest

def test_announce_routes(fib):
    """Simple test case that utilize fib to announce route in order to a newly setup test bed receive
       BGP routes from remote devices
    """
    assert True

Q&A

Q: Why not use exabgp to advertise routes directly to the DUT? A: Yes, we can. But, we could not simulate the BGP over LAG as there is no LAG protocol running inside the PTF docker.