[dhcwg] Re: DHCP behind NAT
Bernard Dugas <bernard.dugas@is-production.com> Wed, 29 August 2001 09:42 UTC
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Date: Wed, 29 Aug 2001 11:32:17 +0200
From: Bernard Dugas <bernard.dugas@is-production.com>
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To: ietf-web@ietf.org, Ralph Droms <rdroms@cisco.com>, michael.patrick@motorola.com, dhcwg@ietf.org
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Subject: [dhcwg] Re: DHCP behind NAT
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Hello, I've had no comment on that. Is it the right procedure ? The patch is loadable at http://www.is-pronet.com/download/, with the original version and the patched version of ISC dhcpd we were using. Best regards, and thanks for help of mailing lists and open source process ! Bernard Dugas a écrit : > > Hi, > > I have a comment to do on both RFC : > - Dynamic Host Configuration Protocol (RFC 2131); > - DHCP Relay Agent Information Option (RFC 3046). > > I couldn't find in these RFC's any mention of the possibility of a DHCP > client being on a subnet behind some NAT device like a router. > > NAT is used quite often, specially in the kind of network represented in > RFC3046 Figure 1 page 3, with network clients behind modems. > > Even more, it seems that the behaviour described by RFC2131 > is preventing a dhcp server to answer to a client behind a NAT. > > 3 problems have been identified : > - PB1) In the case of a unicast DISCOVER, with a relay involved, the > DHCP > server is answering to the ip address of the relay (giaddr field). In a > non-NAT context, the giaddr is the same that the source ip address of > the DISCOVER packet. But with NAT, the DHCP server MUST answer to the IP > source address of the DISCOVER packet. This problem may happen also in > other requests. > > cf. " If the 'giaddr' field in a DHCP message from a client is > non-zero, > the server sends any return messages to the 'DHCP server' port on the > BOOTP relay agent whose address appears in 'giaddr'. " > in : > " Droms Standards Track [Page > 23] > RFC 2131 Dynamic Host Configuration Protocol March 1997 > " > > - PB2) The same apply for to UDP port of the OFFER packet : it should be > the udp port of the IP source address of the DISCOVER packet, because > NAT may have changed the port too ; > > - PB3) The DHCP server is issuing a ICMP echo on client address before > answering with the OFFER. In a NAT context, the echo can't go on the > client subnet. The RELAY should do the ping before relaying the OFFER. > > To illustrate the PB1, I can send you a patch on ISC dhcp 3.0.RC11, > which allow our DHCP server to answer to clients behind NAT. > > I would be very grateful to have an answer on these problems. Thanks a > lot. -- __________ Bernard DUGAS ________________________________________ | | | Technoparc Pays de Gex mailto:bernard.dugas@is-production.com | | 30 Rue Auguste Piccard Tel.: +33 450 205 105 | | FR 01630 St Genis Pouilly Fax : +33 450 205 106 | |_________________________________________________________________| _______________________________________________ dhcwg mailing list dhcwg@ietf.org http://www1.ietf.org/mailman/listinfo/dhcwg
- [dhcwg] Re: DHCP behind NAT Bernard Dugas
- Re: [dhcwg] Re: DHCP behind NAT Ted Lemon
- Re: [dhcwg] Re: DHCP behind NAT Bernard Dugas
- Re: [dhcwg] Re: DHCP behind NAT Ted Lemon