[nycbug-talk] FreeBSD Dual homed

Thu Dec 20 23:21:59 EST 2007

On Dec 20, 2007 9:26 PM, Brian McGonigle <brian.mcgonigle at gmail.com> wrote:
> I just figured it was worth a try :-). Someone mentioned they were DSL lines
> and I thought the MTU would've been lower on a DSL interface. I've never
> used FreeBSD with DSL so it was just a guess. It sounds like you're right
> though.
>
> We can't get PMTU on FreeBSD to work over the GRE tunnels between our data
> centers. I've ran tcpdumps while transferring files and can see the ICMP
> "destination unreachable, need to fragment" packets but FreeBSD doesn't seem
> to do anything about them. On the other hand, a linux box on the same subnet
> can transfer to the same destination. Actually, the only time FreeBSD does
> work over the tunnels is when transferring to a linux box. My theory is that
> linux is properly discovering the MTU and FreeBSD is getting the lower MTU
> during the tcp handshake. If I'm wrong, I'd like to start a new thread
> because I'd love to find a better fix than disabling PMTU.
>
> On Dec 20, 2007 8:35 PM, Trish Lynch <trish at bsdunix.net> wrote:
> > What does PMTU discovery have anything to do with the dual homes box - I
> think the one thing to try is enabling source routing.
> >
> > See - you can only have one default route - so all traffic only passes out
> one interface, when connecting to the other - the one without the route, the
> packets try and go out the *default* route instead of being routed out of
> the interface the connection is on.
> >
> > Turn on net.inet.ip.sourceroute,  net.inet.ip.accept_sourceroute, and
> net.inet.ip.forwarding and I bet it will work.

Trish-

That's a no go, I enabled in /etc/sysctl.conf and rebooted.

net.inet.ip.sourceroute=1
net.inet.ip.accept_sourceroute=1
net.inet.ip.forwarding=1

> >
> > (You can also use some other trickery as well, but this is more "correct",
> and yes I'm aware of the implications aregarding spoofed packets, but in
> order to be able to arbitrarily choose the route to use, these need to be
> anabled)
> >
> > FWIW , I've seen path MTU discovery work just fine on FreeBSD unless
> someone has blocked the ICMP packets needed for it to work. (Type 3, code
> 4). Most of the problems people report with PMTU are people being for lack
> of a better term, *clueless* and filtering ICMP indiscriminately. I'd still
> like to know what MTU has to do with the ability to not route over a certain
> network.
> >
> > -Trish
> > --
> > Trish Lynch
> > M: 646-401-1405
> > H: 201-378-0434
> >
> >
> > -----Original Message-----
> > From: "Brian McGonigle" <brian.mcgonigle at gmail.com >
> >
> > Date: Thu, 20 Dec 2007 20:19:35
> > To:talk at lists.nycbug.org
> > Subject: Re: [nycbug-talk] FreeBSD Dual homed
> >
> >
> > Try lowering the MTU or disabling PMTU discovery. I have never seen PMTU
> discovery work on FreeBSD. I always use a lower MTU when going over a WAN.
> >
> >
> >
> > On Dec 20, 2007 4:24 PM, Rodrique Heron < swygue at gmail.com
> <mailto:swygue at gmail.com> > wrote:
> >
> >
> >
> > Dan Langille wrote:
> > > ... I think I misunderstood you in my original reply.
> > >
> > > Rodrique Heron wrote:
> > >> Hello all-
> > >>
> > >> Are there any known issues when FreeBSD is dual homed.
> > >
> > > There may be issues, but I have run dual homed FreeBSD since 1998.
> > >
> > >
> > >> I have two interfaces, each connected to a different subnet. Whenever
> > >> both are enabled I can't get any incoming network traffic to the
> server.
> > >
> > > Can you elaborate upon this? It's not clear what you are trying to do.
> > >
> > > So one NIC fails to work? No traffic in or out? Both nics?
> > >
> > > Output of netstat -na would help us understand.
> > >
> > > > I'm not
> > >> routing between the two, therefore no "gateway_enable" in rc.conf. I
> > >> don't have any firewalls enabled, I do have my defaultrouter set.
> > >
> > > I originally said:
> > > AFAIK, you cannot route between the two UNLESS you have
> > > gateway_enable="YES" in /etc/rc.conf.
> > >
> > > But what you mean is that you do not wish to route between the two
> > > subnets. The FreeBSD box is not a gateway. It is merely dual homed.
> > >
> > >
> > >
> > >
> > Hope this helps-
> >
> >
> > # sockstat -4
> > root sendmail 628 3 tcp4 127.0.0.1:25 <http://127.0.0.1:25>   *:*
> >
> > root sshd 609 4 tcp4 *:22 *:*
> >
> >
> >
> >
> >
> > # ifconfig -a
> >
> > em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
> >
> >   options=b<RXCSUM,TXCSUM,VLAN_MTU>
> >
> >   inet
> > 150.210.240.36 <http://150.210.240.36>  netmask 0xffffff00 broadcast
> 150.210.240.255 < http://150.210.240.255>
> >
> >
> >   ether 00:14:22:23:1a:2e
> >
> >   media: Ethernet autoselect (1000baseTX <full-duplex>)
> >
> >   status: active
> >
> > em1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
> >
> >   options=b<RXCSUM,TXCSUM,VLAN_MTU>
> >
> >   inet
> > 150.210.160.243 <http://150.210.160.243>  netmask 0xffffff00 broadcast
> 150.210.160.255 <http://150.210.160.255>
> >
> >
> >   ether 00:14:22:23:1a:2f
> >
> >   media: Ethernet autoselect (1000baseTX <full-duplex>)
> >
> >   status: active
> >
> > lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
> >
> >   inet6 fe80::1%lo0 prefixlen 64 scopeid 0x3
> >
> >   inet6 ::1 prefixlen 128
> >
> >   inet
> > 127.0.0.1 <http://127.0.0.1>  netmask 0xff000000
> >
> >
> >
> >
> >
> > # arp -an
> >
> > ? (150.210.160.204 < http://150.210.160.204> ) at 00:00:5e:00:01:04 on em1
> [ethernet]
> >
> > ? (
> > 150.210.160.214 < http://150.210.160.214> ) at 00:0b:db:90:73:1f on em1
> [ethernet]
> >
> > ? (150.210.160.227 <http://150.210.160.227 > ) at 00:11:43:ef:ba:36 on em1
> [ethernet]
> >
> > ? (
> > 150.210.160.254 <http://150.210.160.254> ) at 00:00:0c:07:ac:04 on em1
> [ethernet]
> >
> > ? (150.210.240.32 <http://150.210.240.32> ) at 00:0c:29:62:78:63 on em0
> [ethernet]
> >
> > ? (
> > 150.210.240.39 <http://150.210.240.39> ) at 00:0c:29:f8:e7:2c on em0
> [ethernet]
> >
> > ? (150.210.240.55 < http://150.210.240.55> ) at 00:1a:64:24:ce:bc on em0
> [ethernet]
> >
> >
> >
> >
> >
> >
> > # netstat -rn -f inet
> >
> > Routing tables
> >
> >
> >
> > Internet:
> >
> > Destination Gateway Flags Refs Use Netif Expire
> >
> > default 150.210.160.254 <http://150.210.160.254>   UGS 0 415 em1
> >
> > 127.0.0.1 <http://127.0.0.1>   127.0.0.1 <http://127.0.0.1>   UH 0 0 lo0
> >
> >
> > 150.210.160/24 link#2 UC 0 0 em1
> >
> > 150.210.160.204 <http://150.210.160.204>   00:00:5e:00:01:04 UHLW 1 18 em1
> 552
> >
> > 150.210.160.214 <http://150.210.160.214>   00:0b:db:90:73:1f UHLW 1 5 em1
> 654
> >
> > 150.210.160.227 <http://150.210.160.227>   00:11:43:ef:ba:36 UHLW 1 3 em1
> 747
> >
> > 150.210.160.254 <http://150.210.160.254>   00:00:0c:07:ac:04 UHLW 2 0 em1
> 547
> >
> >
> > 150.210.240/24 link#1 UC 0 0 em0
> >
> > 150.210.240.32 <http://150.210.240.32>   00:0c:29:62:78:63 UHLW 1 6 em0
> 547
> >
> >
> > 150.210.240.39 <http://150.210.240.39>   00:0c:29:f8:e7:2c UHLW 1 12 em0
> 547
> >
> > 150.210.240.55 < http://150.210.240.55>   00:1a:64:24:ce:bc UHLW 1 8 em0
> 743
> >
> >
> >
> >
> >
> >
> >
> > _______________________________________________
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> >
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> >
> >
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>
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-- 
swygue neron --->>