Slow transfer speeds over different subnets

[synertecadmin]

Hello,

We are running out of IP Addresses in our DHCP scope, so I have been tasked with sorting this out. One possible solution we are considering is to setup a second scope and use Superscoping.

Our main IP range is 192.168.0.0/24 and we would like to use 192.168.1.0/24 for the next range.

We use Cisco Switches Catalyst 2960 which are Gb devices and Juniper SRX firewalls. We also have a layer 3 switch a Catalyst 3650, which we are using for test purposes.

On the layer 3 switch, I created 2 vLans for the 2 different IP ranges and can successfully get traffic flowing between the 2 networks. I have also created address book entries on the Juniper firewall and set a trust to trust policy to handle the routing.

As a test, I have been copying a 4GB file between devices on the same IP range and also between the 2 networks.

Typically, the file will transfer in about 40 seconds at speeds of 100MB/sec between devices on the same network. However, when copying this file between the 2 networks then I get a massive reduction in transfer speed.

The cisco layer 3 switch gets a transfer rate of around 20MB/sec and when using the Juniper device instead I get a speed of 10MB/sec.

If I connect my test clients directly to the layer 3 switch then I get a transfer speed of 100MB/sec which is what I would expect. However, when I connect the clients to a normal switch which in turn gets connected to the layer 3 switch, then my transfer speed drops to 20MB/sec

All ports are set to their full speed of 1Gb.

Is Superscoping not a good idea. We really do not want to change to a /23 subnet, but it looks like this might be our next option if I cannot get the routing between 2 networks to work at an acceptable speed. Bearing in mind that this is only a test setup so there is no traffic on the network, apart from the 2 test clients

[synertecadmin]

> check if the L2 switch also knows about the different VLANs?

It doesn't I have not configured anything on the L2 switch I am using for testing

[synertecadmin]

another thing
is the vlan2 IP configured as default gateway for vlan2 clients
and the vlan3 IP for the vlan3 clients?

Yes that's correct I have set the default gateway to be 192.168.0.1 and 192.168.1.1 for the vlan clients respectively

[synertecadmin]

-> Yes, now the switch only has two addresses to connect to for management using telnet/ssh it does not use it to forward packets between vlan2 and vlan3 and it will not build the normal "ARP-table" to look up MAC-adresses for an IP-adress.

Sorry to be dumb, i'm quite new to networking as you can tell :)

What do I need to do then to fix it?

Show IP Route shows the following:

Switch#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override

Gateway of last resort is not set

      192.168.0.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.0.0/24 is directly connected, Vlan2
L        192.168.0.1/32 is directly connected, Vlan2
      192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.1.0/24 is directly connected, Vlan3
L        192.168.1.1/32 is directly connected, Vlan3
Switch#

[Georg Pauwen]

Hello,

--> I have not setup any IP Routing on the L3 switch,

Your switch is configured with 'ip routing'. In order to avoid further confusion, post a schematic drawing of your topology and indicate how the two clients in different VLANs are connected...

[synertecadmin]

[Georg Pauwen]

The ports on the L2 switch need at a minimum to be configured as access ports in the assigned VLAN. What do you mean it has no config info ?

[synertecadmin]

An earlier post asked -> check if the L2 switch also knows about the different VLANs? 

What I mean by the L2 switch has no config is that I have not configured them with any of the VLANs or as per your post I have not configured them as access ports

[Georg Pauwen]

That is why it doesn't work. The ports on your L2 switch default to VLAN 1.

Configure the ports with:

switchport mode access

switchport access vlan 2

spanning-tree portfast

switchport mode access

switchport access vlan 3

spanning-tree portfast

[Richard Burts]

I am a bit late to this discussion. If I am reading it correctly then the transfer does work - it just works slowly. If the problem really had to do with routing not enabled, or vlans not enabled, or something like that it seems to me that the transfer would not work at all. Have I missed something in the discussion?

The point that sticks out to me is the statement that when clients are directly connected to layer 3 switch then transfer is quick but is slow when clients are connected to layer 2 switch, which then connects to layer 3 switch. To me this suggests that there is something about the layer 2 switch or about its connection to the layer 3 switch that is the cause. Can we get info about configuration of layer 2 switch and the output of show interface from the the connected interfaces of both switches?

HTH

Rick

[synertecadmin]

Hi Rick, you are absolutely correct. The transfer works just very slowly. If I connect the clients directly to the L3 switch then I get the correct transfer rate, but when connected to an L2 switch (which connects to the L3 one), then the transfer speed is very slow.

I will post config info from the L2 switch on Monday

[synertecadmin]

I’ve just fixed it😀 the l2 switch had 192.168.0.1 set as an IP Address for vlan1 as soon as I removed that IP Address then I got the correct transfer speed.

I hadn’t thought to check the l2 switch but it had some old config info in it. 

not sure why this has worked but it seems to have fixed it at any rate.

So, currently the only vlan config is set on the l3 switch. The l2 switch makes no reference to VLANs 2 and 3 and it seems to work

[synertecadmin]

Thank you very much to everyone who took the time to reply and thank you for your patience as well

[Alex Pfeil]

A great way to say thank you is to mark replies as helpful!

Thanks!

[Richard Burts]

I am puzzled about the statement that the layer 2 switch makes no reference to vlans 2 and 3 and it works. But if it is working as expected now then that is a good thing. Thanks for the update.

HTH

Rick