Working around cheap SOHO routers under OpenBSD
A friend of mine uses a cheaper home router to handle the connection to his ISP, this device implements a small forwarding DNS server.. but it only listens on UDP.
Protocol limitations documented in RFC1035 mention that a packet received from a UDP DNS server be no greater then 512 bytes in size.. or else the packet is truncated. (Whatever that means..).
You may be asking why this is relevant.. well, he uses OpenBSD as a workstation.. as such he uses Pidgin to connect to Yahoo's servers.
If you dig(1) scs.msg.yahoo.com you'll see how many redundant servers they have.. unfortunately this exceeds the UDP DNS packet limitation and in the case of my friends router makes for a nasty problem.. the domain can't be resolved.
;; Truncated, retrying in TCP mode. ;; Connection to 192.168.1.1#53(192.168.1.1) for scs.msg.yahoo.com failed: connection refused.
1) Use his ISP's servers directly in /etc/resolv.conf
2) Use OpenBSD and replace the SOHO router..
3) Try enabling the edns0 option in /etc/resolv.conf
But naturally.. he chose #3, and it appears to work for him..
Note; dig(1) will still try to use a TCP server if the query is too large.. so use the +ignore option to bypass that.
Last edited by BSDfan666; 23rd November 2008 at 06:40 PM.
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