SIP 483 Too Many Hops
Max-Forwards reached zero before the request reached its target.
4xx Client failure · RFC 3261 · Answer to OPTIONS: Up, but our request passed through too many proxies.
What SIP 483 means
Every SIP request carries a Max-Forwards header, which normally starts at 70. Each proxy that forwards the request lowers it by one, and a proxy that receives it at zero for a target other than itself answers 483. The limit exists so that a request can't circle forever.
A 483 almost always points at a routing loop: two systems, or one system and itself, keep passing the request between them. A legitimate path seldom has more than a handful of hops. RFC 3261 also lets a proxy answer an OPTIONS that arrives with Max-Forwards at zero itself, which is a way to probe one specific hop.
Example response
SIP/2.0 483 Too Many Hops
Via: SIP/2.0/UDP 203.0.113.50:5060;branch=z9hG4bK-483-s9
Via: SIP/2.0/UDP 203.0.113.51:5060;branch=z9hG4bK-483-s8
Via: SIP/2.0/UDP 203.0.113.50:5060;branch=z9hG4bK-483-s7
From: <sip:+[email protected]>;tag=d33f
To: <sip:+[email protected]>;tag=mh-0a
Call-ID: [email protected]
CSeq: 2 INVITE
Content-Length: 0Common causes of SIP 483
- The SBC sends calls for a number range to the PBX, and the PBX's default route sends them straight back to the SBC.
- Two proxies each treat the other as the next hop for the same destination, often after a routing change.
- A call forwarding rule points a number at itself, directly or through another number.
- The request started with a low Max-Forwards value, so even a normal path used it up.
How to fix SIP 483
- Look at the Via headers in the request or the 483: the same addresses appearing again and again show the loop.
- Check the default or catch-all routes on each system in the loop; one of them sends back what it received.
- Make sure the PBX rejects numbers it doesn't own instead of returning them to the trunk.
- Check the Max-Forwards value your system puts on new requests; it should normally be 70.
SIP 483 as an answer to OPTIONS
A 483 to OPTIONS means the server is up, but the probe passed through too many proxies before it reached its target, which suggests a loop on the server's side. A PingVo Route counts it as reachable by default, since something answered, but the same loop will affect calls.
Questions about SIP 483
What is the difference between SIP 482 and 483?
482 Loop Detected means a server saw the same request come back through itself. 483 means the hop counter ran out, which is how loops that slip past loop detection end.
Can I use Max-Forwards to test one hop?
Often. RFC 3261 allows a proxy that receives an OPTIONS with Max-Forwards at zero to answer it itself, so the response tells you about that hop alone. Not every proxy does it.