Packet routing

[jpadie]

I am concerned about some bottlenecks in my network and would just like to check a very basic premise about routers.

currently my topology looks like this

internet (adsl) gateway & router (dhcp enabled)
-> wifi/wired router (acting in bridge mode)
-> devices
-> bridge (powerline 200Mb/s)
-> router
-> devices

the gateway is 100Mb/s, the wifi router is 802.11n + gigabit and the router on the other side of the bridge is a 100Mb.

my question is whether the data will still route always via the router (and thus have to go on the slow 100Mb/s link) or whether tcp/ip is intelligent enough to know that there is a more direct/faster route to take? the reason behind the question is that there is little point in upgrading the last router to gigabit, and hardwiring the current powerline connection if i can expect no speed advantage. at that point it would be better to re-examine the whole topology. gigabit ethernet is preferable as there is HD video and multi gig (100+) files being thrown around the network all the time.

each router is a retail item rather than a pro equivalent. the gateway is supplied by the ISP (unavoidable as telephony and television are also provided by the same box). the main AP is an airport extreme and the internal router on the far side of the bridge is a decent netgear 24 port thing with a fan that's about as noisy as a newborn babe with croup.

your expertise will be greatly appreciated.

 

[burtsbees]

So, the switch (what you call a bridge) is before the router???

This looks like a flat network, with only one possible path to devices. Not sure what you are asking, but you are as fast as your slowest link, and switching occurs between devices on the same subnet---routing does not occur until there is a separate broadcast domain, at L3...

/

tim@tim-laptop ~ $ sudo apt-get install windows
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package windows...Thank Goodness!

 

[jpadie]

So, the switch (what you call a bridge) is before the router???

yes. essentially i have two sides of the premises joined by the powerline. each side has a bunch of devices wired in to the router on that side and one side also has a wifi AP.

there is only one dhcp provider and all devices are operating on the 192.168.1.x 255.255.255.0 subnet.

i could separate the subnets but then the time machine and other in-lan services get upset by the double NAT. i tried setting a DMZ on the internet gateway pointing to the AP (which i figured should work) but this did not tick the box. i have not been able to diagnose why.

but you are as fast as your slowest link

so take, for example, one side of the LAN where there is a gigabit router and 3 devices connected (all gigabit). those three devices will communicate at 100Mb rather than gigabit speeds because the whole LAN is slowed down by the ADSL gateway that is acting as the DNS provider and DHCP? i'm assuming the fact that all devices are macs and use mDNS makes no difference here either?

 

[burtsbees]

What is the reason for two routers?

Everything on the same subnet will operate at the fastest switched speed---they are not getting routed if they are on the same subnet. The only thing a router will do for layer 2 and layer 3 is pass packets from one subnet/network to another. I use the term subnet loosely here---in this instance, it means all within the same block of addresses.

I guess you'll have to provide a visio or a better ASCII topology here, and some reason why you have it like this. Is the adsl gateway router also a switch?

The best way to do things here, if you are simply trying to separate things, is to get a router that can connect to the modem, or has a built-in modem, and a switch that can support vlans, and separate everything, each "premis", into its own vlan.

A Cisco 1721 with a WIC-1ADSL and a Cisco Catalyst 2924 would be perfect.

Please specify what types/brands of router/"bridge" everything is...

/

tim@tim-laptop ~ $ sudo apt-get install windows
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package windows...Thank Goodness!

 

[jpadie]

thanks Tim. i don't have a proper flow charting piece of software but i will draw the topology out carefully and upload it as an image later today. i will also research the term /switch/router/bridge in the hopes that i will use it correctly and not confuse!

back later.