limit¶

Enforce prefix length and count limits.

Synopsis¶

bgpipe [...] -- limit [OPTIONS]

Description¶

The limit stage enforces constraints on BGP UPDATE messages to prevent prefix flooding attacks (such as the Kirin attack). It tracks announced prefixes and drops messages that violate configured limits.

The stage supports three types of count limits:

Session limit (--session): maximum total prefixes across the session
Origin limit (--origin): maximum prefixes per origin AS
Block limit (--block): maximum prefixes per IP address block

Prefix length limits (--min-length, --max-length) reject individual prefixes that are too specific or too broad.

Use --ipv4 and/or --ipv6 to select which address families to process. If neither is specified, only IPv4 is processed. Use separate limit stages for different limits on IPv4 and IPv6.

The stage tracks prefix state across the session lifetime, correctly handling both announcements and withdrawals (unless --permanent is set).

This stage supports bidirectional operation with -LR, aggregating counts from both directions. Without -LR, it tracks only the stage direction.

Options¶

Option	Type	Default	Description
`-4`, `--ipv4`	bool	`false`	Process IPv4 prefixes (default if neither -4 nor -6 given)
`-6`, `--ipv6`	bool	`false`	Process IPv6 prefixes
`--multicast`	bool	`false`	Include multicast address families
`--permanent`	bool	`false`	Ignore withdrawals (announcements are permanent)
`-m`, `--min-length`	int	`0`	Minimum prefix length; 0 disables
`-M`, `--max-length`	int	`0`	Maximum prefix length; 0 disables
`-s`, `--session`	int	`0`	Global session prefix limit; 0 disables
`-o`, `--origin`	int	`0`	Per-AS origin prefix limit; 0 disables
`-b`, `--block`	int	`0`	Per-IP-block prefix limit; 0 disables
`-B`, `--block-length`	int	`0`	IP block prefix length (max 64); 0 means /16 (IPv4) or /32 (IPv6)

Events¶

The stage emits events prefixed with limit/ when limits are violated:

Event	Trigger
`limit/short`	Prefix shorter than `--min-length`
`limit/long`	Prefix exceeds `--max-length`
`limit/session`	Session prefix count exceeds `--session`
`limit/origin`	Per-origin prefix count exceeds `--origin`
`limit/block`	Per-block prefix count exceeds `--block`

Use --events limit/session on bgpipe to log these events, or --kill limit/session to terminate the session when a limit is hit.

Examples¶

Enforce standard prefix length limits for IPv4 and IPv6:

bgpipe --kill limit/session \
    -- connect 192.0.2.1 \
    -- limit -LR -4 --min-length 8 --max-length 24 --session 1000000 \
    -- limit -LR -6 --min-length 16 --max-length 48 --session 250000 \
    -- connect 10.0.0.1

Limit per-origin AS prefix count (detect prefix hijack floods):

bgpipe --events limit/origin \
    -- connect 192.0.2.1 \
    -- limit -LR --origin 5000 \
    -- connect 10.0.0.1

Limit per /16 block (IPv4) to detect concentrated floods:

bgpipe \
    -- connect 192.0.2.1 \
    -- limit --block 10000 --block-length 16 \
    -- connect 10.0.0.1