From: Ben (bmunyao@gmail.com)
Date: Tue Jul 31 2007 - 10:23:16 ART
Just when i thought I had it figured. What happens at ARP level?
Just to break it down.
1. Host in vlan1 sends ARP broadcast.
2. broadcast flooded to all vlan1 ports, including port with cable
interconnecting vlan1 to vlan2.
3. afaik, vlan2 port should drop the broadcast. Now I'm not sure what
happens at this stage.
assuming we put aside our routing knowledge for a moment:
4.If broadcast flooded through vlan2, destination host receives it and
unicasts its IP back.
5. Unknown unicast flooded to all vlan2 ports including interconnection
port.
6 host in vlan1 caches entry and sends unicast data. Or does it? When it
detects the source as being from another IP subnet, shouldn't it drop the
arp response packet? If from same subnet, it will accept the entry.
7 If same subnet, indeed they should communicate. If not, I'm not sure what
happens next.
Perhaps someone else can demystify this communication further.
Ben
On 7/31/07, Carlos G Mendioroz <tron@huapi.ba.ar> wrote:
>
> Hmm, you are for a surprise if you think so.
> Yes, this works, and there are some setups where this may prove useful.
>
> Like some switches that only support one private vlan promiscuous port
> and you need to connect a couple.
> Or some restrictions on where you can rate limit on some architectures.
> (E.g. you can go to a real L3 interface from a L2 access)
>
> Nothing really clean, and I would not recomend doing that anywhere, but
> works... like most hacks.
>
> -Carlos
>
> Ben @ 31/07/2007 07:13 -0300 dixit:
> > Martijn,
> >
> > VLANs by design confine traffic to the vlan, unless it has been routed
> > across to another vlan. Merely connecting a cable between two VLANs
> > therefore does not circumvent this behavior, even if hosts in the two
> vlans
> > use the same IP subnet.
> >
> > Ben
> >
> >
> > On 7/31/07, martijn <groupstudy@martijnj.nl> wrote:
> >> Lim,
> >>
> >> i needed to laugh a little at first. Never tried.
> >>
> >> Not THE answer, I think you need to test.
> >>
> >> let's break up your q's.
> >>> done before?
> >> No.
> >>> Can a host on VLAN359 now communicate with a host on VLAN360?
> >> After i read your post trice, i see you want to do it @ one switch.
> when i
> >> want to do comms with an host it starts with ip, if that is not local
> >> (logical AND) I go for the default gateway. Do your pc's have
> >> one?????????????
> >>
> >> When I look to your Q form another angle, say mac-addr table, (never
> >> tested,
> >> group?) I would say mac-addr binding goes to direct connected prot
> first,
> >> after that I assume that the link would for a L2 link between vlan's.
> Any
> >> takes?
> >>
> >> martijn
> >>
> >> ----- Original Message -----
> >> From: "Toh Soon, Lim" <tohsoon28@gmail.com>
> >> To: <ccielab@groupstudy.com>
> >> Sent: Tuesday, July 31, 2007 9:43 AM
> >> Subject: Bridging VLANs by looping cable
> >>
> >>
> >>> Hi All,
> >>>
> >>> This may sound simple and mundane but for curiosity sake, I need to
> seek
> >>> clarification.
> >>>
> >>> Has anyone tried "bridging" two VLANs by looping a cable to the same
> >>> switch?
> >>> E.g. in the following diagram:
> >>>
> >>> Gi0/1(VLAN359)----
> >>> |
> >>> |
> >>> Gi0/2(VLAN360)----
> >>>
> >>> The same cable connects to interfaces Gi0/1 (VLAN359) and Gi0/2
> >> (VLAN360).
> >>> Can a host on VLAN359 now communicate with a host on VLAN360?
> >>>
> >>> What's the implication doing this, e.g. from STP point of view? Is it
> >>> recommended at all?
> >>>
> >>> Any advice is appreciated.
> >>>
> >>>
> >>> Thank you.
> >>>
> >>> B.Rgds,
> >>> Lim TS
> >>>
> >>>
> _______________________________________________________________________
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> >
> > _______________________________________________________________________
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> >
>
> --
> Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
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