arista-evpn-vxlan-clab/docs/HOST_INTERFACE_CONFIGURATION.md

Host Interface Configuration Guide

Overview

All four hosts in the lab use persistent interface configuration files mounted via ContainerLab's binds feature. This approach provides cleaner, more maintainable configuration compared to using exec commands.

Architecture

Dual-Homing with LACP Bonding

Each host is dual-homed to an MLAG pair of leaf switches:

• host1: dual-homed to leaf1 + leaf2 (VTEP1)
• host2: dual-homed to leaf3 + leaf4 (VTEP2)
• host3: dual-homed to leaf5 + leaf6 (VTEP3)
• host4: dual-homed to leaf7 + leaf8 (VTEP4)

VLAN Configuration

Hosts handle VLAN tagging using sub-interfaces on the bond:

Host	VLAN	IP Address	Purpose	VRF
host1	40	10.40.40.101/24	L2 VXLAN test	default
host2	34	10.34.34.102/24	L3 VXLAN test	gold
host3	40	10.40.40.103/24	L2 VXLAN test	default
host4	78	10.78.78.104/24	L3 VXLAN test	gold

Interface Files Structure

Each host has a configuration file in hosts/ directory:

• hosts/host1_interfaces → mounted to /etc/network/interfaces in host1
• hosts/host2_interfaces → mounted to /etc/network/interfaces in host2
• hosts/host3_interfaces → mounted to /etc/network/interfaces in host3
• hosts/host4_interfaces → mounted to /etc/network/interfaces in host4

Interface Configuration Format

Example: host1_interfaces

auto lo
iface lo inet loopback

# Bond interface with LACP (802.3ad)
auto bond0
iface bond0 inet manual
    bond-mode 4
    bond-miimon 100
    bond-lacp-rate 1
    bond-slaves eth1 eth2

# VLAN 40 on bond0
auto bond0.40
iface bond0.40 inet static
    address 10.40.40.101
    netmask 255.255.255.0
    vlan-raw-device bond0

Key Parameters Explained

Bond Configuration:

• bond-mode 4: LACP (802.3ad) mode - requires LACP on switch side
• bond-miimon 100: Link monitoring interval (100ms)
• bond-lacp-rate 1: Fast LACP (1 second intervals)
• bond-slaves eth1 eth2: Physical interfaces in the bond

VLAN Sub-interface:

• bond0.40: VLAN interface notation (bond0.VLAN_ID)
• vlan-raw-device bond0: Parent interface for VLAN
• Static IP configuration with address/netmask

Deployment Process

When ContainerLab starts a host:

1. Mount interface file via binds
2. Install packages: apk add ifupdown bonding vlan
3. Load kernel modules:
   • modprobe bonding - enables LACP bonding
   • modprobe 8021q - enables VLAN tagging
4. Bring up interfaces: ifup -a reads /etc/network/interfaces

Switch Configuration Requirements

For proper LACP operation, leaf switches must have:

interface Port-Channel1
   description host-X
   switchport mode trunk
   switchport trunk allowed vlan <vlan-id>
   mlag 1
   port-channel lacp fallback timeout 5
   port-channel lacp fallback individual
   no shutdown

interface Ethernet1
   description host-X-link1
   channel-group 1 mode active
   lacp timer fast
   no shutdown

Critical settings:

• port-channel lacp fallback: Required for ContainerLab timing
• lacp timer fast: Matches host's fast LACP rate
• no shutdown: Must explicitly enable Port-Channel interface

Advantages of This Approach

1. Persistence: Configuration survives container restarts
2. Clarity: Single file shows complete network config
3. Maintainability: Easy to modify VLAN assignments
4. Production-like: Mirrors real-world dual-homing scenarios
5. Clean deployment: No manual post-deployment fixes needed

Testing Connectivity

L2 VXLAN (same VLAN)

# host1 (VLAN 40) → host3 (VLAN 40)
docker exec clab-arista-evpn-fabric-host1 ping -c 4 10.40.40.103

L3 VXLAN (inter-VRF)

# host2 (VLAN 34, VRF gold) → host4 (VLAN 78, VRF gold)
docker exec clab-arista-evpn-fabric-host2 ping -c 4 10.78.78.104

Troubleshooting

Verify bond status on host

docker exec clab-arista-evpn-fabric-host1 cat /proc/net/bonding/bond0

Check VLAN interface

docker exec clab-arista-evpn-fabric-host1 ip addr show bond0.40

Verify LACP on switch

ssh admin@clab-arista-evpn-fabric-leaf1 "show port-channel 1 detailed"

References

• Alpine Linux ifupdown-ng documentation
• Linux bonding documentation: /usr/src/linux/Documentation/networking/bonding.txt
• Arista MLAG configuration guide
• srl-labs/srl-evpn-mh-lab (reference implementation)