DNS Round-Robin for IRC: Load Balancing Without a Load Balancer

When you type irc.libera.chat into your client, you expect to reach a server. You don't expect to choose which server. Behind that hostname sits DNS round-robin — a load distribution mechanism older than most IRC users. It has no health checks, no session awareness, and no intelligence whatsoever. It also works remarkably well for IRC's specific use case.

The Single Hostname Problem

An IRC network with five servers needs one entry point. You could publish all five hostnames and let users choose, but that creates an uneven distribution (everyone picks the first one on the list) and a terrible user experience (which server do I pick?). What you want is a single hostname — irc.yournetwork.org — that magically distributes connections across all servers.

Commercial services solve this with hardware or software load balancers. IRC networks, run by volunteers with zero budget, solve it with DNS. The technique predates IRC itself — the concept of multiple A records for one hostname was used for early web server farms in the 1990s. But IRC adopted it early and comprehensively.

How DNS Round-Robin Works

DNS round-robin is deceptively simple. You create multiple A (or AAAA) records for the same hostname, each pointing to a different server IP:

irc.example.net.    300    IN    A    198.51.100.1
irc.example.net.    300    IN    A    198.51.100.2
irc.example.net.    300    IN    A    198.51.100.3
irc.example.net.    300    IN    A    198.51.100.4

When a client resolves irc.example.net, the DNS server returns all four addresses. The order rotates with each query (this is the "round-robin" part). Most clients try the first address in the response. Since the order changes per query, different clients end up connecting to different servers.

This is not true load balancing. There is no awareness of server load, no connection counting, no health monitoring. A server could be down, overloaded, or on fire, and DNS will happily continue directing clients to it. Despite this, it works for IRC because:

• IRC connections are long-lived (hours to days). Initial distribution matters more than per-request balancing.
• IRC clients typically try all resolved addresses if the first fails. Most modern clients implement connection fallback.
• IRC server capacity tends to be roughly equal across a network.

BIND Configuration for IRC

A typical BIND zone file for an IRC network:

$TTL 300

@ IN SOA ns1.example.net. admin.example.net. (
    2024011501 ; Serial
    3600       ; Refresh
    900        ; Retry
    604800     ; Expire
    300        ; Minimum TTL
)

@ IN NS ns1.example.net.
@ IN NS ns2.example.net.

; IRC round-robin pool
irc     IN A     198.51.100.1    ; server1 - Frankfurt
irc     IN A     198.51.100.2    ; server2 - Amsterdam
irc     IN A     198.51.100.3    ; server3 - London
irc     IN A     203.0.113.10    ; server4 - New York

; IPv6 pool
irc     IN AAAA  2001:db8::1     ; server1
irc     IN AAAA  2001:db8::2     ; server2
irc     IN AAAA  2001:db8::3     ; server3
irc     IN AAAA  2001:db8::4     ; server4

; Individual server hostnames (for direct connections and server linking)
server1 IN A     198.51.100.1
server2 IN A     198.51.100.2
server3 IN A     198.51.100.3
server4 IN A     203.0.113.10

; TLS SRV records (IRCv3)
_ircs._tcp IN SRV 0 0 6697 irc.example.net.

TTL Strategy and Failover

The TTL (Time To Live) value controls how long resolvers cache the DNS response. For IRC round-robin, this involves a tradeoff:

• Low TTL (60-300s): Faster failover when you remove a dead server. More DNS queries hitting your nameservers. Resolvers may round-robin more effectively since they re-query frequently.
• High TTL (3600s+): Less DNS traffic. Slower failover — clients may keep trying a dead server for up to an hour. Some resolvers cache indefinitely regardless of TTL.

Most IRC networks use a TTL between 300 and 600 seconds. This gives a reasonable failover window — remove the dead server's record, and within 10 minutes most new connections will stop trying it. Existing connections are unaffected; they're already established.

Failover for existing connections is handled at the IRC level, not DNS. When a user's server goes down, their client detects the disconnection and reconnects — this time resolving the hostname again and (hopefully) getting a working server. The user experiences a brief disconnection, but the recovery is automatic.

Limitations You Will Hit

No health checking. If a server crashes, DNS continues advertising its IP. Clients that resolve the dead server's IP first will experience a connection timeout (typically 30-60 seconds) before trying the next address. Some clients handle this gracefully. Others don't.

Resolver caching is unpredictable. Your ISP's DNS resolver, Google's 8.8.8.8, Cloudflare's 1.1.1.1 — they all cache differently. Some respect TTL. Some impose minimum TTLs. Some cache for hours regardless of what you specify. You cannot rely on consistent propagation timing.

Uneven distribution. Round-robin gives you rough distribution, not exact distribution. Some servers will have 30% more connections than others due to caching patterns, resolver behavior, and geographic clustering of users. For IRC, this is usually acceptable.

No geographic awareness. A user in Tokyo may resolve a server in Frankfurt first. Their latency will be terrible. Standard DNS round-robin has no concept of "send this user to the nearest server."

Alternatives: Anycast, GeoDNS, HAProxy

GeoDNS solves the geographic problem. Services like PowerDNS with GeoIP backend, or managed DNS providers like Cloudflare or Route53, can return different IP addresses based on the querier's location. European users get European servers. Asian users get Asian servers. The configuration is more complex but the user experience improves dramatically.

Anycast is the nuclear option. The same IP address is announced from multiple locations via BGP. Routing protocols direct traffic to the nearest announcement point. Large networks like Libera.Chat use anycast for their main hostname. The downside: you need your own AS number and BGP peering arrangements, which puts it out of reach for small networks.

HAProxy or similar TCP proxies can sit in front of IRC servers, providing true load balancing with health checks. The proxy accepts connections, checks which backend servers are healthy, and forwards the connection. This adds latency and a single point of failure (the proxy itself), but provides capabilities that DNS can't: connection draining, active health monitoring, and weighted distribution.

# HAProxy TCP frontend for IRC
frontend irc_frontend
    bind *:6667
    bind *:6697 ssl crt /etc/haproxy/certs/irc.pem
    default_backend irc_servers

backend irc_servers
    balance leastconn
    option tcp-check
    server irc1 198.51.100.1:6667 check
    server irc2 198.51.100.2:6667 check
    server irc3 198.51.100.3:6667 check

For most volunteer-run IRC networks, DNS round-robin remains the right answer. It costs nothing, requires no additional infrastructure, and handles the typical scale of modern IRC traffic. Save the fancy solutions for when you actually need them.

Monitoring Your Round-Robin Health

Since DNS round-robin has no built-in health checking, you need external monitoring. A simple approach is a cron job that tests TCP connectivity to each server in the pool and alerts when one is unreachable:

#!/bin/bash
# check_irc_pool.sh — Run every 5 minutes via cron
SERVERS="198.51.100.1 198.51.100.2 198.51.100.3 203.0.113.10"
PORT=6697

for ip in $SERVERS; do
    if ! timeout 5 bash -c "echo > /dev/tcp/$ip/$PORT" 2>/dev/null; then
        echo "IRC server $ip:$PORT is DOWN" | mail -s "IRC Pool Alert" admin@example.net
    fi
done

More sophisticated setups use monitoring systems like Prometheus with blackbox_exporter to track connection success rates, latency, and TLS certificate expiry for each server in the pool. The key metric is connection establishment time — if a server responds but takes 10 seconds to accept a TCP connection, it might as well be down from a user perspective.

Some networks automate DNS record management: when monitoring detects a dead server, a script removes the corresponding A record via DNS API (Cloudflare, Route53, PowerDNS HTTP API). When the server recovers, the record is re-added. This gives you poor man's health-checked load balancing using nothing but DNS and a shell script. It is ugly. It works.