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An alternative Cilium Egress Gateway that removes state synchronization and conntrack overhead in active-active multi-gateway setups from the gateway

I lost an afternoon to a “routing loop” that turned out not to be a loop at all. It was an EVPN all-active multihoming feature quietly not working in a virtual lab — and the packets ping-ponging between two switches were a symptom, not the disease. This post is two things: a refresher on how Arista ESI (Ethernet Segment) multihoming actually forwards traffic, and a write-up of the specific trap you can fall into when you build EVPN designs on vEOS/containerlab instead of real hardware. ...

Dual-homed servers use IP-unnumbered physical interfaces. A dedicated dummy interface (not lo) is assigned to each server as its IPv4 node address. FRR runs between the servers and the ToR switches to provide node-level connectivity, advertising the server’s node IP (dummy interface address) and receiving the default route from the ToRs. Using a bond interface between ToRs can also be used for redundancy and failover for server connectivity. You may also configure Layer 3 interfaces. The main issue is about node identity and service continuity during the failure of a single link. Using a bond interface or a dummy interface seems like a more usable approach. ...

ESI Multi-Homing and ARP Suppression Issue: Duplicate Packets & Flooding When ESI is not functioning correctly, you may observe duplicate packets destined for hosts behind the ESI. Remote switches might flood traffic toward the ESI switches instead of handling it efficiently. TCAM Carving for ARP Suppression To use the suppress-arp feature effectively and prevent unnecessary flooding, you must allocate sufficient TCAM resources on the switch hardware. 1 2 3 # Configure TCAM carving for ARP suppression hardware access-list tcam region racl 512 hardware access-list tcam region arp-ether 256 double-wide Warning: It was observed that enabling suppress-arp caused reachability and ARP resolution to break between hosts when attempting to use RFC 5549 (BGP Unnumbered / IPv6 underlay) between Spines and Leafs for IPv4 and EVPN. Note that an IPv6 underlay is generally not supported for Cisco Nexus 9300/9500v platforms in this context. ...

Overview This document outlines the security policies and dynamic routing configurations for the network gateway, including firewall rules via nftables and BGP peering via BIRD. How Zones are Defined and Connected In this architecture, zones (zone_blue, zone_green, zone_red, and wan) directly correspond to network interfaces (either physical NICs, VLAN tags, or bridge interfaces) on the Gateway Server. Chain Structure (nftables): The firewall strictly controls traffic flow by matching the input interface (iif) and output interface (oif). For example, iif zone_blue oif zone_green tcp dport 22 accept explicitly states: If a packet enters the server via the zone_blue interface and is destined to leave via the zone_green interface on TCP Port 22, allow it. ...

Overview This document describes a method for simulating multiple servers belonging to different network domains on a single Linux host. Each simulated server runs inside its own Linux network namespace and is connected to a dedicated VLAN. Training and demonstration environments Each namespace behaves as an independent server with: Its own IP address Its own MAC address An SSH service A simple HTTP server Network Topology The Linux host uses the following interfaces: ...

We run multiple teams on the same OpenStack platform, one project per team. Traffic between two projects always hairpins through the gateway nodes, even with DVR enabled. This is expected behavior, not a misconfiguration. Below is the technical summary of why. What DVR distributes East-west between networks on the same router: routed locally on the ingress chassis, tunneled to the destination chassis. Fully distributed. North-south with a floating IP: the chassis hosting the VM performs the 1:1 NAT and answers ARP for the FIP on the external network. Distributed, but requires the provider network to be attached to every compute node and distributed FIP to be enabled. North-south with SNAT: centralized. The router’s external address is shared by all VMs behind it; it can be ARP-owned at only one point of the external segment, and the NAT state must live in a single conntrack table. It is pinned to a gateway chassis by design. DVR distributes only what it can bind 1:1 to a single chassis. Everything based on a shared, stateful address is centralized. ...

Why anycast inside the fabric is harder than it looks An anycast service is advertised from multiple hosts into the data center fabric — the same prefix, the same service IP, originated from several places at once. The promise is appealing: multiple next hops for one service prefix gives you load balancing, fast failover, and horizontal scalability without any state in the network. The catch is that for every leaf to actually use all of those origins, the fabric has to carry and install multiple equal-cost paths for a single prefix end to end. That is not BGP’s default behavior, and the moment you combine it with two things modern fabrics love — an IPv6 unnumbered underlay and IPv4-in-IPv6 next hops (RFC 5549) — one of the most common EVPN disambiguation tricks stops working. This post walks through why, and what the realistic options are. ...

Companion posts. This is the hands-on lab — real NX-OSv configs, the tests I ran, and where they broke. For the high-level summary see Anycast Inside the Data Center; for the deeper protocol write-up (overlay index, recursive resolution, why pure-IP fabrics lose per-host ECMP) see Anycast in EVPN/VXLAN Fabrics: The IPv6 Unnumbered and RFC 5549 Problem. Why Anycast is used for horizontal scaling and for better failure response. With modern orchestration and virtualization, a new instance of a service can be spawned on demand — by an engineer or by the system itself. ...

Part of an anycast series. This is the high-level summary. For the hands-on NX-OS lab (configs, the RFC 5549 failure, the working EVPN solution) see Anycast Inside an EVPN/VXLAN Fabric with BGP Unnumbered (RFC 5549), and for the deeper protocol treatment see Anycast in EVPN/VXLAN Fabrics: The IPv6 Unnumbered and RFC 5549 Problem. Why Anycast services are advertised from multiple hosts into the data center. The same service prefix is originated from several places at once, which gives you multiple next hops for that service — and with it, load balancing, better failover, and scalability. ...