wmgwd2

README

wmgwd2

wmgwd2 is a distributed gateway daemon for WiMoVE. I wrote this daemon as part of my bachelor's thesis.

The design of wmgwd2 is inspired by VRRP. In VRRP, there needs to be one virtual router per overlay network. This results in many messages that are sent between the gateways. wmgwd2 aims to use a single peer discovery mechanism for all overlay networks.

Architecture

wmgwd2 assumes that all gateways are in one L2 domain. Each wmgwd2 process periodically broadcasts UDP packets to the hard-coded address 10.0.1.255. Each UDP packet contains an 8-byte unique ID. Gateways listen for the messages of other gateways.

Using highest random weight hashing (also known as rendezvous hashing), each wmgwd2 process determines which gateway is responsible for a given overlay network. wmgwd2 then reconciles the network configuration with the determined assignment.

wmgwd2 sends periodic gratuitous ARP responses. Therefore, a running instance of FRR advertises BGP EVPN routes as needed.

When a gateway fails, its wmgwd2 process is not able to send periodic advertisements. Other processes recognize the failure, recompute the assignments and change their network state.

Configuration

Name	Default	Explanation
uid		Unique ID used in advertisements
minvni	1	Minimum VXLAN Network Identifier
maxvni	100	Maximum VXLAN Network Identifier

Network Configuration

wmgwd2 depends on a proper network interface configuration. The program requires a macvlan interface on which it sets the protodown flag as required. The interface name is hardcoded to vrrp4-%d where %d is replaced with the VNI.

FRR requires a VXLAN interface with a bridge interface for BGP EVPN operations. They can be coupled to the macvlan interface via a virtual Ethernet interface. For VNI 100, the resulting network interface structure looks like this:

Currently, wmgwd2 does not support IPv6 interfaces, so vrrp100-6 need not exist.

An example FRR configuration that can be used with wmgwd2 looks like this:

ip forwarding
ip nht resolve-via-default
ip6 nht resolve-via-default
router bgp 65000
  bgp router-id 10.0.1.11
  no bgp default ipv4-unicast
  neighbor fabric peer-group
  neighbor fabric remote-as 65000
  neighbor fabric capability extended-nexthop
  neighbor fabric ebgp-multihop 5
  neighbor fabric timers 1 3
  neighbor 10.0.1.17 peer-group fabric
  address-family l2vpn evpn
   neighbor fabric activate
   advertise-all-vni
   advertise-svi-ip
  exit-address-family
  !
!
router ospf
 ospf router-id 1.1.1.1
 network 0.0.0.0/0 area 0.0.0.0
!