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Beginner

Subnet mask 255.255.255.255 by DHCP

Hi

I'tried to connect my Netgear 3G modem in bridge mode to an Cisco ISR4331 on Gi0/0/1 configured as DHCP adressing.

When I connect the 3G modem to PC's, then I got the public address and a subnet mask of 255.255.255.255 - It is working at my PC and I have access to the internet.

I tried to set the ISR to manual IP adressing, with the public IP with the subnet mask of 255.255.255.255.

 

I look like that the ISR doesn't accepts 255.255.255.255 as subnet mask, either if it's assigned static or from DHCP - what to do then?

/Michae

9 REPLIES 9
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VIP Mentor

Re: Subnet mask 255.255.255.255 by DHCP

Based on the Post your PC able to get DHCP IP from router.

 

So i suggest to configure router Interface to DHCP, so you get DHCP IP from router ( since we do not know how the DCHP Server configured other side)

 

Hope this is test router then below steps  should work.

 

Config t
!
Default interface Gi 0/
0/1
!
interface Gi 0/0/1
ip addres dhcp
no shutdown
end
!
wr


check the Router has DHCP IP address from DHCP

 

From router you should be able to ping 8.8.8.8 or 1.1.1.1

 

Test and Advise.

BB
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Highlighted
Beginner

Re: Subnet mask 255.255.255.255 by DHCP

Hi
Unfortunately the router don't get IP address if assigned to DHCP client.
Show, ip, int, br show that the link is up but interface IP is unassigned.

Br,
Michael
Highlighted
VIP Mentor

Re: Subnet mask 255.255.255.255 by DHCP

Thats odd, When you connect PC, you get same IP address all the time, 

 

Debug on router, also try dot1q config on router to see is there any tagging VLAN ?

 

Check the Logs when you shut and unshut the interface(enabling debug)

 

 

 

BB
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Highlighted
Beginner

Re: Subnet mask 255.255.255.255 by DHCP

Yes - I can connect different PC - all get the sam public IP.

The ISR don't get any address at all.

 

When trying to set the adress manually with the subnet mask of 255.255.255.255 - it's not possible?

Is ther som limitations in IOS XE?

 

/MR

Highlighted
VIP Mentor

Re: Subnet mask 255.255.255.255 by DHCP

I do not believe interface have capabilites to take 255.255.255.255 mask (i never done that in real world) 

we can only set that mask for loopback.

 

other hand will your ISP allow you to set the IP address manually ?  may be try with 255.255.255.252 nearest mask and see if that work.

 

if not i would stil go route of debugging enable ?

 

BB
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VIP Mentor

Re: Subnet mask 255.255.255.255 by DHCP

Hello

Why do you need the modem in bridge mode, you could have the modem in router mode and still bridge that connection on you ISR?



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future
Highlighted
Beginner

Re: Subnet mask 255.255.255.255 by DHCP

Hi
I don't think it's a right solution. I have to configure a temporary site2site VPN connection - until the customers ISP can install a fixed fiber connection-
Highlighted
VIP Mentor

Re: Subnet mask 255.255.255.255 by DHCP

Hello

Possibly try using a subinterface on the ISR 

example:
int gig x/x/x-1
enacpsulation dotq 1
ip address dhcp

 

Also the modem may be locked down to registered a single max-address of a connected host, So to negate this you could spoof the mac-address of the connected pc and assign it to the ISR wan interface and see if you then obtain address allocation

int gig x/x/x
mac address xxxx.xxxx.xxx - (pc mac address)
ip address dhcp



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future
Highlighted
Beginner

Re: Subnet mask 255.255.255.255 by DHCP

First thing is that on a router interface we cannot use /32 Subnetmask 

 

IOU3(config-if)#ip address 12.0.0.1 255.255.255.255
Bad mask /32 for address 12.0.0.1

 

Try capturing the packet in the link between router interface to the modem and see anything happening.

Please do not hesitate to click the STAR button if you are satisfied with my answer.