Re: probably an easy routing question, so please help
- From: "stephen" <stephen_hope@xxxxxxxxxxxx>
- Date: Thu, 17 May 2007 11:56:33 GMT
"Trendkill" <jpmason@xxxxxxxxx> wrote in message
news:1179328714.470756.105670@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On May 16, 9:57 am, pk <philip.kl...@xxxxxxxxx> wrote:for
On May 15, 2:55 pm, Trendkill <jpma...@xxxxxxxxx> wrote:
On May 15, 3:33 pm, pk <philip.kl...@xxxxxxxxx> wrote:
I'm not routing master, so this might be obvious, but I've been
curious about the answer to this question. Say an individual was
issued two IP blocks from their ISP.
IP Block 1 : 123.123.123.0 /28
IP Block 2 : 123.123.123.128 /28
If the individual doesn't really care to separate the two networks
ofany reason and was just unfortunately issued two /28 blocks instead
sufferone /27 block, isn't the link between the two networks going to
theunnecessarily? For instance, if Server A located in Block 1 is
plugged into the same gigabit switch as Server B in Block 2 and they
want to initiate a file transfer, they are required to run out to
todefault gateway (ISPs router) through a T1 (perhaps) connection and
back in when it would have been much faster for them to go directly
case,the other's gigabit ethernet port on the switch? If this is the
thewould this be remedied, albeit poorly, by just subnetting both of
these ranges together into one giant class C address range? (I
understand fully that they wouldn't be able to access the rightful
owners of the rest of the IP addresses in that range as they would
search on their local LAN for them and time out, but this is a
hypothetical situation and only serves to educate myself on the
concept.) That said, how SHOULD this be handled in order to keep
connection between the subnets optimal?
I'm quite sure that I'm missing some key concepts here, so please be
kind and explain them to me.
Thanks.
pk
Provided both of those networks are off the same edge router, and
routing is enabled, the traffic will not have to go across the WAN/
Internet link, and will instead route to the directly connected
network. This should work without issue.
OK, that makes sense, but if the uplink is coming out of the switch
from a 10Mb link to the router and the computers are both hooked into
gigabit ports then it is a big difference right? There's no way for
that switch to be a bit smarter (without turning into a router) and
not run out the 10Mb port to the router with all of its traffic,
correct? Whereas before they would have transferred at gigabit rate,
they now will be 100 times slower?
Technically yes you are correct. Unless you have a L3 switch or a
router with gig ports, you will potentially have limits for any
bandwidth going inter VLAN. I've been trying to think through your
option of running a /24 behind the scenes and simply not addressing
nodes in the two networks you don't own.
you can use proxy ARP to do this. i leant this trick on Bay / Nortel kit
which was really good at it, but it works on Cisco as well.
both /28s are configured on the same Enet port, with proxy ARP enabled.
end stations are set up to use the overall /24.
The router then lets local ARP take care of traffic between the 2 /28s, but
will respond to ARP reqs for addresses on other parts of the /24.
Once the ARP table is pointing at the correct device, then IP packets get
sent to the right place - result is the router has a bit more broadcasts to
handle, but the local traffic doesnt need to "touch" the router.
I'm not really sure if this
would work or not, as it your router technically would have to
advertise the /24, unless of course you could use distribution lists
or something to split it up as necessary. I think your best bet is to
sit down and really analyze your servers/nodes and come up with a
design that keeps your high traffic boxes on one switch/subnet or the
other. I doubt you have 126 boxes that are the same application, etc,
and probably could be split into some kind of logical groups by high
traffic. Thus ensuring that intra VLAN traffic is maximized, and
inter-vlan traffic is minimized. If you do have a server (database or
such) that is central to both networks, perhaps its better to just
dual home it to each network. All depends on your requirements......
Personally i prefer a L3 switch - a single Catalyst 3560 or 3750 will give
you enough ports for both /28s.
if you have enough servers to need 2 x /28, then paying for the switch is
going to be trivial. And if you dont need lots of servers, then redo the
design to use NAT and reduce the number of needed addresses.
clever system designs can be great, but follow on work often hits side
effects, or the next engineer to do changes doesnt understand and breaks the
design....
--
Regards
stephen_hope@xxxxxxxxxxxx - replace xyz with ntl
.
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