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Gateways & Routing

Virgin Media Fiber:

  • 1Gbit/s down
  • 100Mbit/s up
  • XGS-PON (10-Gigabit-capable passive optical network; 10 Gbit/s shared symmetric capacity)
  • MTU: 1468 1460,
  • no IPv4 on router - IPv6 DS-Lite (IPv4 tunneled in IPv6 to DS-Lite carrier-grade NAT), 
  • no router bridge mode.

MTU

From VPS:

ping -s 1472 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 1472(1500) bytes of data.
1480 bytes from 8.8.8.8: icmp_seq=1 ttl=110 time=1.34 ms

From router itself max ping size 1440 (IP packet size: 1468).

From network (via Caroline/no VPN):

ping -s 1440 57.128.183.232
PING 57.128.183.232 (57.128.183.232) 1440(1468) bytes of data.
1448 bytes from 57.128.183.232: icmp_seq=1 ttl=48 time=25.1 ms

Router configuration:

  • Gateway MTU size    2000 (1280-1500) ???
    • When set to 1500 MTU drops to 1460 and I cannot go back! They took 8 byte WTF is this?!?!?!
      • Looks like I was getting extra 8 bytes (1508) with 2000 setting.

IPv6 header occupies 40 bytes so IPv4 in IPv6 gets 1500 - 40 = 1460 MTU.

Two gateways

There are two gateways on the network:

  1. caroline - exposed to the internet, provides access to internet and forwards connections to servers in SERVER VLAN
  2. justine - VPN G/W that connects to Mullvad and terminates incoming WireGuard VPN connections

Clients use caroline as G/W for direct internet access and justine as G/W for Mullvad protected internet access. Additionally caroline runs DNS server that uses the ISP DNS server, while justine will use PiHole and Mullvad's DNS server.

Routing with two gateways

Things get very complicated with two gateways setup. Clients need to be able to direct traffic to correct gateway in response to connections coming from one or the other gateway.

Gateway forwarded connections:

  1. caroline forwards from the internet to access internal network to:
    1. public SERVER network services from outside: blog, younohost etc.
    2. justine WireGuard VPN
  2. justine forwards from internet VPN connected devices  to:
    1. HOME network
    2. to caroline for SERVER network

This creates the challenge where devices can be configured with any G/W and need to be able to forward the traffic to the other G/W in some cases:

  1. local IP & bridge - VPN clients could be bridged directly and assigned bridged network IP
  2. NAT - packets coming into the network are MASQUERADE'd to G/W IP address (how it is done currently)
  3. static route - push static routes to all clients so response to packets coming from G/W terminated IPs (e.g. VPN) are forwarded back to correct G/W
  4. ICMP redirect - both G/W could be configured to inform clients on the correct G/W to use for packets destination

Problems:

  • NAT will obscures the source IP address making troubleshooting, monitoring and accounting more difficult.
  • Static routes or redirects will work if G/W can be deduced from destination IP address.
  • ICMP redirects many not work reliably, will probably drop first packet?
  • Pushing routes to clients requires client support, NAT makes things transparent to clients.

Server VLAN

Uses dedicated VM server-gw that uses WireGuard VPN to connect to Vps server. It acts as default G/W for all SERVER VLAN hosts and routes traffic out via Vps over the VPN connection. This way all servers have Vps public IP as their outgoing IP.

Incoming traffic is forwarded by Vps over same VPN connection to server-gw and from there to www for HTTP(S) termination and also to younohost service for Jitsi meet streams.

Sanbox VM network

Igor runs dedicated network (vnet) with sanbox-gw instance acting as default G/W for VMs connected to it. It runs Mullvad VPN and this way provides private connectivity out to the internet. There is no port forwarding into the network. The network is isolated from all other networks.

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