BGP over TLS/TCP

Introduction The Border Gateway Protocol (BGP) relies on the TCP protocol to establish BGP sessions between routers. A recent draft has proposed to replace TCP with the QUIC protocol . QUIC brings many features compared to TCP including security, the support of multiple streams or datagrams. From a security viewpoint, an important benefit of QUIC compared to TCP is that QUIC by design prevents injection attacks that are possible when TCP is used by BGP . Several techniques can be used by BGP routers to counter this attacks . TCP-AO authenticates the packets exchanged over a BGP session provides similar features as QUIC. However, it is notoriously difficult to configure the keys used to protect BGP sessions. The widespread deployment of TLS combined with the possibility of deriving TCP-AO keys from the TLS handshake creates an interest in using TLS to secure BGP sessions. This document describes how BGP can operate over TCP/TLS.

Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. This document uses network byte order (that is, big endian) values. Fields are placed starting from the high-order bits of each byte.

Summary of operation A BGP over TLS/TCP session is established in two phases:

establish a transport layer connection using TCP
establish a TLS session over the TCP connection

The TCP connection SHOULD be established on port TBD1. During the establishment of the TLS session, the router that initiates the connection MUST use the "botls" token in the Application Layer Protocol Negotiation (ALPN) extension . The support for other ALPN MUST NOT be proposed during the TLS handshake. Once the TLS handshake is established and finished, the BGP session is initiated as defined in and the protocol operates in the same way as a classic BGP over TCP session. The difference is that the BGP session is now encrypted and authenticated using the TLS layer. As in , the TLS authentication parameters used for this connection are out of the scope of this draft. A first implementation of BGP over TLS/TCP was demonstrated in .

Security Considerations This document improves the security of BGP sessions since the information exchanged over the session is now protected by using TLS. If TLS encounters a payload injection attack, it will generate an alert that immediately closes the TLS session. The BGP router SHOULD then attempt to reestablish the session. However, this will cause traffic to be interrupted during the connection re-establishement. If both BGP peer supports TCP-AO, the TLS stack is protected against payload injection and this attack can be avoided. When enabled, TCP-AO counters TCP injection attacks listed in . Furthermore, if the BGP router supports TCP-AO, we recommend an opportunistic TCP-AO approach as suggested in . The router will attempt to connect using TCP-AO with a default key. When the TLS handshake is finished, the routers will derive a new TCP-AO key using the TLS key. TCP-MD5 MAY be used to protect the TLS session if TCP-AO is not available on the BGP router. The use of certificates to secure BGP raises operational concerns. ASes MAY trust external actors and use their certificates for authentication. The provisioning of BGP over TLS/TCP certificates and some alternatives to using certificates will be discussed in another companion draft.

IANA Considerations IANA is requested to assign a TCP port (TBD1) from the "Service Name and Transport Protocol Port Number Registry" as follows:

Service Name: botls
Port Number: TBD1
Transport Protocol: TCP
Description: BGP over TLS/TCP
Assignee: IETF
Contact: IDR WG
Registration Data: TBD
Reference: this document
Unauthorized Use Reported: idr@ietf.org

It is suggested to use the same port as the one selected for BGP over QUIC .

Acknowledgments The authors thank Dimitri Safonov for the TCP-AO implementation in Linux.

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