update¶

Modify UPDATE message attributes.

Synopsis¶

bgpipe [...] -- update [OPTIONS]

Description¶

The update stage modifies BGP UPDATE messages in-flight, with the route policy actions common in production networks: rewrite next-hops, add, remove or scrub communities, prepend or clean the AS_PATH, set MED, LOCAL_PREF and ORIGIN, and drop unwanted attributes. Non-UPDATE messages pass through unchanged.

This stage supports bidirectional operation with -LR. Without -LR, it applies only to messages in the stage direction. Combine with --if to apply modifications only to messages matching a filter.

Options¶

Next-hop¶

Option	Type	Default	Description
`--nexthop4`	string		Set next-hop for IPv4 prefixes to this address
`--nexthop6`	string		Set next-hop for IPv6 prefixes to this address
`--nexthop-self`	bool	`false`	Set next-hop to our own IP address (when available)

Communities¶

Option	Type	Default	Description
`--add-com`	string		Add a standard BGP community (`ASN:value`)
`--add-com-ext`	string		Add an extended BGP community (JSON, see below)
`--add-com-large`	string		Add a large BGP community (`G:L1:L2`)
`--drop-com`	bool	`false`	Remove the COMMUNITY attribute entirely
`--drop-com-ext`	bool	`false`	Remove the EXT_COMMUNITY attribute entirely
`--drop-com-large`	bool	`false`	Remove the LARGE_COMMUNITY attribute entirely
`--del-com`	strings		Remove matching communities (CSV); `` matches any value, eg. `65000:`
`--del-com-large`	strings		Remove matching large communities (CSV), eg. `65000::`

Unlike its siblings, --add-com-ext takes the JSON object format used in the EXT_COMMUNITY attribute output, e.g. '{"type": "TARGET", "value": "65000:100"}' (or a JSON array of such objects).

For each attribute, drop takes precedence: when both --drop-com* and the matching --add-com* are given, the attribute is dropped and the add is ignored. --del-com* runs after --add-com*.

AS_PATH¶

Option	Type	Default	Description
`--prepend`	strings		Prepend given ASN(s) to the AS_PATH (CSV, in order), eg. `65000,65000`
`--prepend-first`	int	`0`	Prepend the first (neighbor) ASN given number of times (0-32)
`--strip-private`	bool	`false`	Remove private ASNs (RFC 6996) from the AS_PATH

--prepend-first is applied before --prepend, eg. --prepend-first 2 --prepend 65000 turns 3549 3356 into 65000 3549 3549 3549 3356. AS_SET segments are left as-is. All AS_PATH actions assume 4-byte ASN sessions (the norm): on legacy 2-byte sessions, AS4_PATH is not modified.

Other attributes¶

Option	Type	Default	Description
`--set-med`	int		Set MULTI_EXIT_DISC (MED) to given value
`--drop-med`	bool	`false`	Remove the MED attribute (takes precedence over `--set-med`)
`--set-localpref`	int		Set LOCAL_PREF (only meaningful towards iBGP peers)
`--set-origin`	string		Set ORIGIN: `igp`, `egp`, or `incomplete`
`--drop-attr`	strings		Remove given attributes (CSV of names or codes), eg. `OTC,28`

Message size¶

An edit can grow an UPDATE past the maximum BGP message size: 4096 bytes, or 65535 if Extended Message (RFC 8654) was negotiated. Since sending it would reset the session downstream, such an UPDATE is converted into a withdrawal of its prefixes instead (with a warning).

Messages without reachable prefixes (pure withdrawals) are passed through unmodified: per RFC 4271 section 4.3, a withdrawal must not carry path attributes.

Examples¶

Rewrite next-hop for all updates:

bgpipe \
    -- connect 192.0.2.1 \
    -- update --nexthop4 10.0.0.1 \
    -- connect 10.0.0.1

Add a community to tag traffic from a specific peer:

bgpipe \
    -- connect 192.0.2.1 \
    -- update --add-com 65000:100 \
    -- connect 10.0.0.1

Strip all communities before forwarding:

bgpipe \
    -- connect 192.0.2.1 \
    -- update --drop-com --drop-com-ext --drop-com-large \
    -- connect 10.0.0.1

Conditionally modify: add a community only to RPKI-invalid updates:

bgpipe \
    -- connect 192.0.2.1 \
    -- rov --invalid keep \
    -- update --if 'tag[rov/status] == INVALID' --add-com 65000:666 \
    -- connect 10.0.0.1

Set next-hop to self (useful when proxying):

bgpipe \
    -- listen :179 \
    -- update --nexthop-self \
    -- connect 192.0.2.1

Scrub your own (eg. informational or action) communities received from external peers, and strip private ASNs leaked by a customer:

bgpipe \
    -- connect 192.0.2.1 \
    -- update --del-com '65000:*' --del-com-large '65000:*:*' --strip-private \
    -- connect 10.0.0.1

Traffic engineering: make routes towards a peer less attractive by prepending our ASN twice, and announce a lower preference via MED:

bgpipe \
    -- listen --peer 10.0.0.1 :179 \
    -- update -L --prepend 65000,65000 --set-med 100 \
    -- connect 192.0.2.1

Graceful shutdown before maintenance (RFC 8326): tag all routes with GRACEFUL_SHUTDOWN so that peers depreference them:

bgpipe \
    -- connect 192.0.2.1 \
    -- update --add-com 65535:0 \
    -- connect 10.0.0.1

Drop optional attributes known to break older routers (eg. attribute 28):

bgpipe \
    -- connect 192.0.2.1 \
    -- update --drop-attr 28 \
    -- connect 10.0.0.1