Chapter 10: VRouter

VRouter and VRouter Agent runs in COMPUTE.


  • vhost0 is a tap interface between host-os and vrouter. vhost0 is the layer-3 interface used by host operating system. As part of setup, Contrail software migrates the IP configuration from ethernet port to vhost0.

  • When networking stack of host-os sends packet on the vhost0 interface, they are received by vrouter module. Vrouter in turn routes the packet. When vrouter needs to send packet to networking stack of host-os, it transmits then through vhost0 interface.

  • pkt0 is the tap interface between vrouter and vrouter-agent.

  • Vrouter traps packets needing control processing such as flow-setup on this interface. Also, when agent uses the pkt0 interface to transmit control packets (ARP for example).

VRF (Virtual Routing and Forwarding)

  • A VRF is created for each Virtual Network.
  • Each VRF consists of 4 Routing Tables - ucindex(unicast), mcindex, l2index, u6index routing tables.
  • VRF Name(default-domain:default-project:ip-fabric:__default__) for physical network/host VRF. This VRF is used for routing the data out to the internet/receives from it. Mostly it match with the routing table output .

vrfstats utility display the vrf statistics

[email protected]:~$ sudo vrfstats  --get 1
Vrf: 1
Discards 0, Resolves 0, Receives 0, L2 Receives 0, Vrf Translates 0, Unknown Unicast Floods 0
Ecmp Composites 0, L2 Mcast Composites 0, Fabric Composites 0, Encap Composites 0, Evpn Composites 0
Udp Tunnels 0, Udp Mpls Tunnels 0, Gre Mpls Tunnels 0, Vxlan Tunnels 0
L2 Encaps 0, Encaps 2
GROs 0, Diags 0
Arp Virtual Proxys 0, Arp Virtual Stitchs 0, Arp Virtual Floods 0, Arp Physical Stitchs 0, Arp Tor Proxys 0, Arp Physical Floods 0

[email protected]:~$

Routing Tables:

There are 4 routing table types, Unicast, Multicast, L2, IPv6 unicast. These routing tables are associated with the VRF,

Let us have a closer look on the unicast routing tables.

Routing tables(Private Network -

  • entry for linklocal (To be confirmed)
  • - discard
  • - pkt0 (pkt0 is for vrouter agent -proxy for gateway)
  • - pkt0 (pkt0 is for vrouter agent - proxy dhcp server )
  • 192.168.14 -- tap interface (VM)

Public Network (external network -

  • default route ( -- vgw (virtual gatway)
  • entry for link local (To be confirmed)
  • -- discard
  • -- pkt0
  • -- pkt0
  • -- VM tap interface (floating IP is associated with a VM)

IP Fabric (Host Routing table)

  • ---- vhost0 --- Vgw (public Network VRF)
  • --- tap interface VM ---- for metadata (we can use this to SSH login to VM as backdoor)
  • ----- local ip vhost0
  • ---- (gw ip)

I have set up the Simple Virtual Gateway, hence vgw interface is created and used. some references.

Flows :

To be updated

VRouter Agent :

VRouter Introspect Port : 8085

In the VRouter introspect, we can get the following important data

Items URL Remarks
VRF LIST http://xxxx:8085/Snh_VrfListReq?name= Lists the VRF, and links to Routing tables, Virtual Network associated to this VRF,
INTERFACE LIST http://xxxx:8085/Snh_ItfReq?name=& Powerful query. List the interfaces with associated VRF, LABELS, VN, VMs, FIP, SG, etc. we can get the complete list


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