Message ID | 159769323.20081014120620@net.ipl.pt |
---|---|
State | Changes Requested, archived |
Delegated to: | David Miller |
Headers | show |
Hi, Pedro Ribeiro <pribeiro-bulk@net.ipl.pt> writes: > Deep analysis in the sources of Linux revealed that the value of > “pref” passed to rt6_add_dflt_router(...) in the file net/ipv6/route.c > isn’t consistent with the one sent by the routers and observed with > wireshark. Seeking the roots of the problem I’ve detected a bug in the > definitions of the bitfield that includes the router preference in the > router advertisement message that are resulting in retrieving the > wrong bits from the structure defined in “include/linux/icmpv6.h”. The > struct is the base one from ICMPv6 (icmp6hdr) and was lacking the bit > field “home_agent” between “router_pref” and “other” and the reserved > bits are only 3, not 4 as in the structure (according to RFC4191) +1 > Follows a “diff” with the changes I’ve made to correct this problem > (I’ve made it against kernel 2.6.23, but I’ve confirmed that the > problem still exists in 2.6.25) > > --- /usr/src/linux-2.6.23-gentoo-r9orig/include/linux/icmpv6.h 2007-10-09 21:31:38.000000000 +0100 > +++ /usr/src/linux-2.6.23-gentoo-r9/include/linux/icmpv6.h 2008-10-13 17:42:56.000000000 +0100 > @@ -40,16 +40,18 @@ > struct icmpv6_nd_ra { > __u8 hop_limit; > #if defined(__LITTLE_ENDIAN_BITFIELD) > - __u8 reserved:4, > + __u8 reserved:3, > router_pref:2, > + home_agent:1, > other:1, > managed:1; > > #elif defined(__BIG_ENDIAN_BITFIELD) > __u8 managed:1, > other:1, > + home_agent:1, > router_pref:2, > - reserved:4; > + reserved:3; > #else > #error "Please fix <asm/byteorder.h>" > #endif Changes look ok to me. > Even after this fix, the problem of deterministic and preference > aware default route selection, remains. I have not figured until now > how the preference affects the selection, maybe it is a missing > feature. can you confirm that you already activated CONFIG_IPV6_ROUTER_PREF in your kernel configuration? What are the values of following parameters on your system?: /proc/sys/net/ipv6/conf/*/accept_ra_rtr_pref /proc/sys/net/ipv6/conf/*/accept_ra_pinfo /proc/sys/net/ipv6/conf/*/accept_ra /proc/sys/net/ipv6/conf/*/autoconf > Developers on this area please clarify me this subject; does the > preference present in the RAs is supposed to influence the decision? Looking at the code in ndisc.c (ndisc_router_discovery()), it should, but I may have missed something. > In addition, what is the criterion for selecting the default route in > the presence of multiple candidates with the same preference? Don't know. Funny it was not detected sooner. In patches I have for UMIP (userland MIPv6 Daemon for Linux), access to router preferences field is done by shifting bits (correctly, AFAICT) and routes are set from userspace using that info. radvd also fills its RA that way, i.e. by shifting bits (it uses struct nd_router_advert from netinet/icmp6.h, which does not have anything for router preference). That would explain why I never hit the bug. Cheers, a+ ps: added YOSHIFUJI Hideaki in CC. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hello Arnaud, Thanks for your quick answer ... Here goes the information solicited. TIA. Tuesday, October 14, 2008, 1:58:41 PM, you wrote: ... > can you confirm that you already activated CONFIG_IPV6_ROUTER_PREF in > your kernel configuration? host ~ # gzip -d -c /proc/config.gz | grep -F CONFIG_IPV6_ROUTER_PREF CONFIG_IPV6_ROUTER_PREF=y > What are the values of following parameters on your system?: > /proc/sys/net/ipv6/conf/*/accept_ra_rtr_pref > /proc/sys/net/ipv6/conf/*/accept_ra_pinfo > /proc/sys/net/ipv6/conf/*/accept_ra > /proc/sys/net/ipv6/conf/*/autoconf All of them have value "1" /proc/sys/net/ipv6/conf/all/accept_ra:1 /proc/sys/net/ipv6/conf/all/accept_ra_defrtr:1 /proc/sys/net/ipv6/conf/all/accept_ra_pinfo:1 /proc/sys/net/ipv6/conf/all/accept_ra_rtr_pref:1 /proc/sys/net/ipv6/conf/default/accept_ra:1 /proc/sys/net/ipv6/conf/default/accept_ra_defrtr:1 /proc/sys/net/ipv6/conf/default/accept_ra_pinfo:1 /proc/sys/net/ipv6/conf/default/accept_ra_rtr_pref:1 /proc/sys/net/ipv6/conf/eth0/accept_ra:1 /proc/sys/net/ipv6/conf/eth0/accept_ra_defrtr:1 /proc/sys/net/ipv6/conf/eth0/accept_ra_pinfo:1 /proc/sys/net/ipv6/conf/eth0/accept_ra_rtr_pref:1 /proc/sys/net/ipv6/conf/lo/accept_ra:1 /proc/sys/net/ipv6/conf/lo/accept_ra_defrtr:1 /proc/sys/net/ipv6/conf/lo/accept_ra_pinfo:1 /proc/sys/net/ipv6/conf/lo/accept_ra_rtr_pref:1 /proc/sys/net/ipv6/conf/all/autoconf:1 /proc/sys/net/ipv6/conf/default/autoconf:1 /proc/sys/net/ipv6/conf/eth0/autoconf:1 /proc/sys/net/ipv6/conf/lo/autoconf:1 Best regards.
From: Pedro Ribeiro <pribeiro-bulk@net.ipl.pt> Date: Tue, 14 Oct 2008 12:06:20 +0100 > Follows a “diff” with the changes I’ve made to correct this problem > (I’ve made it against kernel 2.6.23, but I’ve confirmed that the > problem still exists in 2.6.25) Please make your patch against current sources, it does not apply to the current tree.
--- /usr/src/linux-2.6.23-gentoo-r9orig/include/linux/icmpv6.h 2007-10-09 21:31:38.000000000 +0100 +++ /usr/src/linux-2.6.23-gentoo-r9/include/linux/icmpv6.h 2008-10-13 17:42:56.000000000 +0100 @@ -40,16 +40,18 @@ struct icmpv6_nd_ra { __u8 hop_limit; #if defined(__LITTLE_ENDIAN_BITFIELD) - __u8 reserved:4, + __u8 reserved:3, router_pref:2, + home_agent:1, other:1, managed:1; #elif defined(__BIG_ENDIAN_BITFIELD) __u8 managed:1, other:1, + home_agent:1, router_pref:2, - reserved:4; + reserved:3; #else #error "Please fix <asm/byteorder.h>" #endif