NAT traversal for GIST in 300 seconds A. Pashalidis; H. Tschofenig

{Andreas.Pashalidis, Types of NAT Need to consider different types of NAT, i.e. NAT that 1. modify only IP addresses (“port-preserving”) 2. modify IP addresses and port numbers 3. use a single public IP address 4. dynamically allocate IP addresses to flows 5. are NSIS-aware 1. do not implement the NSLP that is being signalled 2. do implement the NSLP that is being signalled 6. Are NSIS-unaware

{Andreas.Pashalidis, Types of NAT Need to consider different types of NAT, i.e. NAT that 1. modify only IP addresses (“port-preserving”) 2. modify IP addresses and port numbers 3. use a single public IP address 4. dynamically allocate IP addresses to flows 5. are NSIS-aware 1. do not implement the NSLP that is being signalled 2. do implement the NSLP that is being signalled 6. Are NSIS-unaware Draft assumes type (2) and (4) NAT: types (1) and (3) are special cases. Type (6) NATs not (yet?) considered. Cascades of NATs considered, but no “parallel” NATs.

{Andreas.Pashalidis, Two approaches GIST-aware NAT translates GIST header fields (both D and C mode) in a way that is consistent with the translation it applies to the IP header in data flow. GIST-aware NAT adds information into GIST discovery messages; GIST peers then use this information in order to map subsequent signalling to data flows.

{Andreas.Pashalidis, Advantages Signalling messages and data flow consistent throughout the network. NATs remain transparent  NAT-awareness at non-NAT GIST nodes not required. NATs do not “generate mess” that must be “cleaned up” elsewhere. NATs do minimal extra work. Works in the presence of IPsec/TLS.

{Andreas.Pashalidis, Disadvantages Does not work in the presence of IPsec/TLS. NATs need to keep per-flow state (which they do anyway). Non-NAT GIST nodes must be NAT-aware. Internal network details may be revealed to the Internet via the original MRI.

{Andreas.Pashalidis, Disadvantages Does not work in the presence of IPsec/TLS. NATs need to keep per-flow state (which they do anyway). Non-NAT GIST nodes must be NAT-aware. Internal network details are revealed to the Internet via the original MRI. Depending on environment, one approach may be better than the other (?)

{Andreas.Pashalidis, Which approach is taken? Both; depending on whether or not TLS/IPsec is required — NATs transparently maintain consistency throughout Non-NAT GIST nodes less complicated  easier deployment (?) Cascades of NATs handled  easier testing (?) — GIST peers handle NAT-induced inconsistency Necessary in order to provide IPsec/TLS; in such installations GIST peers already interact with IPsec/TLS, key management, OCSP. Thus, NAT handling is another such overhead.

{Andreas.Pashalidis, Scope — Coordination of GIST and address translation in the NAT (NATs are routers too) ? — Coordination of NSLP functionality with NAT functionality (i.e. flow identification before or after translation) ? — Security considerations Installation of bindings as a result of signalling. NAT vs NSIS policies; conflict avoidance ?

{Andreas.Pashalidis, Open issues When should a (bidirectional) NAT binding be installed? — When signalling exists in one direction? — When signalling exists in both directions? — Compatibility with GIST spec — GIST/NSLP unaware NATs

{Andreas.Pashalidis, Conclusion NAT traversal at the GIST layer… — involves addressing many (sub)cases — raises “new” security concerns — is likely to require a document of considerable length Is draft a reasonable basis for further discussion? Feedback solicited!