3750 Routing Questions

[jgorman1977]

I have a 3750 with the enhanced image and am unsure of my interface configurations. Below is my fictional ip block:

External Interfaces

WAN Ethernet: [7.6.5.4]

Default Route for Router: [7.6.5.3]
This will be the path that all of your internet traffic takes to get out to the internet.

Internal Interfaces

Assigned LAN Netblock: [10.9.8.0/24]
Subnet Mask: [255.255.255.0]

LAN Ethernet usable IP's: [10.9.8.2 - 10.9.8.254]
You can use this on your LAN (PC, Workstation, Firewall, etc)

Default Gateway for LAN Netblock: [10.9.8.1]
This will be the IP that all devices use as a default route or gateway for your LAN back to the router.

I have configured gi1/0/1 (WAN Interface) as follows with my default gateway being 7.6.5.3

interface GigabitEthernet1/0/1
no switchport
ip address 207.67.113.246 255.255.255.252
speed 100
duplex full

My question is for the LAN IP's, how do i configure the default gateway for it? Is it just another layer 3 interface? if so, how does it communicate with the WAN default gateway?

Thanks in advance.

[Ganesh Hariharan · Accepted solution]

I have a 3750 with the enhanced image and am unsure of my interface configurations. Below is my fictional ip block:
External Interfaces
WAN Ethernet: [7.6.5.4]
Default Route for Router: [7.6.5.3]
This will be the path that all of your internet traffic takes to get out to the internet.
Internal Interfaces
Assigned LAN Netblock: [10.9.8.0/24] 
Subnet Mask: [255.255.255.0] 
LAN Ethernet usable IP's: [10.9.8.2 - 10.9.8.254]
You can use this on your LAN (PC, Workstation, Firewall, etc) 
Default Gateway for LAN Netblock: [10.9.8.1] 
This will be the IP that all devices use as a default route or gateway for your LAN back to the router.
I have configured gi1/0/1 (WAN Interface) as follows with my default gateway being 7.6.5.3
interface GigabitEthernet1/0/1
 no switchport
 ip address 207.67.113.246 255.255.255.252
 speed 100
 duplex full
My
question is for the LAN IP's, how do i configure the default gateway
for it? Is it just another layer 3 interface? if so, how does it
communicate with the WAN default gateway?
Thanks in advance.

Hi,

If you are trying for internet access or external world access using internal ip address scheme without Natting it wont work.cisco 3750 series does'nt support Nat also.

For your query how routing will be done as 3750 is L3 switch ip routing is enabled in 3750 switches your scenario will be like this

10.9.8.0/24 --- 3750 --7.6.5.4  ----------------7.6.5.3 ISPRouter, You will creating two L3 interface using vlan also or pure L3 port also assign them ip address as dicussed and drop a default route towards the isp router and ask your isp to drop a reverse route towards your L3 switch interface 7.6.5.4. In this way you can have routing between the Routers via your L3.

Hope to Help !!

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Ganesh.H