Solved: Re: Cisco Router can't get out to the internet behind a Comcast Modem

CorporateITGuy · ‎09-21-2021

I am brand new to all things Cisco so apologies for any dumb questions or inability to grasp basic concepts. Trying to set up a cisco router, C897VA-K9, and for some reason I can't even ping dns.google.com from the router with a:

#ping 8.8.8.8

any ideas why? or troubleshooting steps that I can take to figure out what's going on?

Thanks!

Georg Pauwen · ‎09-21-2021

Hello,

add the lines marked in bold to your configuration:

Cisco#show run
Building configuration...

Current configuration : 1996 bytes
!
! Last configuration change at 16:41:34 UTC Tue Sep 21 2021 by corporate
!
version 15.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname Cisco
!
boot-start-marker
boot-end-marker
!
no aaa new-model
!
ip name-server 8.8.8.8
ip name-server 8.8.4.4
ip cef
no ipv6 cef
!
multilink bundle-name authenticated
!
cts logging verbose
license udi pid C897VA-K9 sn FGL220992H6
!
username [removed]
!
controller VDSL 0
!
crypto isakmp policy 1
!
interface ATM0
no ip address
shutdown
no atm ilmi-keepalive
!
interface BRI0
no ip address
encapsulation hdlc
shutdown
isdn termination multidrop
!
interface Ethernet0
no ip address
shutdown
!
interface GigabitEthernet0
no ip address
!
interface GigabitEthernet1
no ip address
!
interface GigabitEthernet2
no ip address
!
interface GigabitEthernet3
no ip address
!
interface GigabitEthernet4
no ip address
!
interface GigabitEthernet5
no ip address
!
interface GigabitEthernet6
no ip address
!
interface GigabitEthernet7
no ip address
!
interface GigabitEthernet8
ip address dhcp
ip nat outside
ip virtual-reassembly in
duplex auto
speed auto
!
interface Vlan1
no ip address
!
interface Vlan10
ip address 192.168.1.1 255.255.255.0
ip nat inside
ip virtual-reassembly in
!
interface Vlan20
ip address 192.168.2.1 255.255.255.0
ip nat inside
ip virtual-reassembly in
!
ip forward-protocol nd
ip http server
ip http authentication local
ip http secure-server
!
--> ip route 0.0.0.0 0.0.0.0 GigabitEthernet8 dhcp
!
--> ip nat inside source list 1 interface GigabitEthernet8 overload
!
--> access-list 1 permit 192.168.1.0 0.0.0.255
--> access-list 1 permit 192.168.2.0 0.0.0.255
!
control-plane
!
mgcp behavior rsip-range tgcp-only
mgcp behavior comedia-role none
mgcp behavior comedia-check-media-src disable
mgcp behavior comedia-sdp-force disable
!
mgcp profile default
!
line con 0
no modem enable
line aux 0
line vty 0 4
login
transport input none
!
scheduler allocate 20000 1000
!
end

View solution in original post

Georg Pauwen · ‎09-21-2021

Hello,

post the full running configuration (show run) of your router...

CorporateITGuy · ‎09-21-2021

Cisco#show run
Building configuration...

Current configuration : 1996 bytes
!
! Last configuration change at 16:41:34 UTC Tue Sep 21 2021 by corporate
!
version 15.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname Cisco
!
boot-start-marker
boot-end-marker
!
!
!
no aaa new-model
!
!
!
!
!
!
!
!
!
!


!
!
!
!
ip name-server 8.8.8.8
ip name-server 8.8.4.4
ip cef
no ipv6 cef
!
!
!
!
!
multilink bundle-name authenticated
!
!
!
!
!
!
!
!
cts logging verbose
license udi pid C897VA-K9 sn FGL220992H6
!
!
username [removed]
!
!
!
!
!
controller VDSL 0
!
!
!
crypto isakmp policy 1
!
!
!
!
!
!
!
!
!
!
interface ATM0
 no ip address
 shutdown
 no atm ilmi-keepalive
!
interface BRI0
 no ip address
 encapsulation hdlc
 shutdown
 isdn termination multidrop
!
interface Ethernet0
 no ip address
 shutdown
!
interface GigabitEthernet0
 no ip address
!
interface GigabitEthernet1
 no ip address
!
interface GigabitEthernet2
 no ip address
!
interface GigabitEthernet3
 no ip address
!
interface GigabitEthernet4
 no ip address
!
interface GigabitEthernet5
 no ip address
!
interface GigabitEthernet6
 no ip address
!
interface GigabitEthernet7
 no ip address
!
interface GigabitEthernet8
 ip address dhcp
 ip nat outside
 ip virtual-reassembly in
 duplex auto
 speed auto
!
interface Vlan1
 no ip address
!
interface Vlan10
 ip address 192.168.1.1 255.255.255.0
 ip nat inside
 ip virtual-reassembly in
!
interface Vlan20
 ip address 192.168.2.1 255.255.255.0
 ip nat inside
 ip virtual-reassembly in
!
ip forward-protocol nd
ip http server
ip http authentication local
ip http secure-server
!
!
ip route 0.0.0.0 0.0.0.0 GigabitEthernet8 3
!
!
!
control-plane
!
!
mgcp behavior rsip-range tgcp-only
mgcp behavior comedia-role none
mgcp behavior comedia-check-media-src disable
mgcp behavior comedia-sdp-force disable
!
mgcp profile default
!
!
!
!
!
!
!
line con 0
 no modem enable
line aux 0
line vty 0 4
 login
 transport input none
!
scheduler allocate 20000 1000
!
!
!
end

Thanks for the quick reply, sorry it took so long.

Georg Pauwen · ‎09-21-2021

Hello,

add the lines marked in bold to your configuration:

Cisco#show run
Building configuration...

Current configuration : 1996 bytes
!
! Last configuration change at 16:41:34 UTC Tue Sep 21 2021 by corporate
!
version 15.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname Cisco
!
boot-start-marker
boot-end-marker
!
no aaa new-model
!
ip name-server 8.8.8.8
ip name-server 8.8.4.4
ip cef
no ipv6 cef
!
multilink bundle-name authenticated
!
cts logging verbose
license udi pid C897VA-K9 sn FGL220992H6
!
username [removed]
!
controller VDSL 0
!
crypto isakmp policy 1
!
interface ATM0
no ip address
shutdown
no atm ilmi-keepalive
!
interface BRI0
no ip address
encapsulation hdlc
shutdown
isdn termination multidrop
!
interface Ethernet0
no ip address
shutdown
!
interface GigabitEthernet0
no ip address
!
interface GigabitEthernet1
no ip address
!
interface GigabitEthernet2
no ip address
!
interface GigabitEthernet3
no ip address
!
interface GigabitEthernet4
no ip address
!
interface GigabitEthernet5
no ip address
!
interface GigabitEthernet6
no ip address
!
interface GigabitEthernet7
no ip address
!
interface GigabitEthernet8
ip address dhcp
ip nat outside
ip virtual-reassembly in
duplex auto
speed auto
!
interface Vlan1
no ip address
!
interface Vlan10
ip address 192.168.1.1 255.255.255.0
ip nat inside
ip virtual-reassembly in
!
interface Vlan20
ip address 192.168.2.1 255.255.255.0
ip nat inside
ip virtual-reassembly in
!
ip forward-protocol nd
ip http server
ip http authentication local
ip http secure-server
!
--> ip route 0.0.0.0 0.0.0.0 GigabitEthernet8 dhcp
!
--> ip nat inside source list 1 interface GigabitEthernet8 overload
!
--> access-list 1 permit 192.168.1.0 0.0.0.255
--> access-list 1 permit 192.168.2.0 0.0.0.255
!
control-plane
!
mgcp behavior rsip-range tgcp-only
mgcp behavior comedia-role none
mgcp behavior comedia-check-media-src disable
mgcp behavior comedia-sdp-force disable
!
mgcp profile default
!
line con 0
no modem enable
line aux 0
line vty 0 4
login
transport input none
!
scheduler allocate 20000 1000
!
end

CorporateITGuy · ‎09-21-2021

Thank you so much! Can you explain to me what those lines did?

--> ip route 0.0.0.0 0.0.0.0 GigabitEthernet8 dhcp

I think this one just made it possible for traffic to get out of the router through g8 right?

--> ip nat inside source list 1 interface GigabitEthernet8 overload

This one I'm not really sure about

--> access-list 1 permit 192.168.1.0 0.0.0.255
--> access-list 1 permit 192.168.2.0 0.0.0.255

and these 2 allow traffic to leave the VLANs right?

Just trying to understand here, thanks again!

Georg Pauwen · ‎09-21-2021

Hello,

exactly. The access lists make sure that the NAT process knows which IP addresses it needs to translate, and the default route sends all traffic out the interface connected to the ISP modem.

CorporateITGuy · ‎09-22-2021

If I wanted to assign a specific IP address as opposed to using DHCP. For example say I have the WAN IP address of 50.50.50.50 and I want all outbound traffic to show like its coming from that address as opposed to the modems 50.50.50.49 like it is with the current configuration. How would I go about that? I would have to edit the static route right?

Georg Pauwen · ‎09-22-2021

Hello,

in that case, you need to change the default route to the next hop. Necessary changes are marked in bold:

Cisco#show run
Building configuration...

Current configuration : 1996 bytes
!
! Last configuration change at 16:41:34 UTC Tue Sep 21 2021 by corporate
!
version 15.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname Cisco
!
boot-start-marker
boot-end-marker
!
no aaa new-model
!
ip name-server 8.8.8.8
ip name-server 8.8.4.4
ip cef
no ipv6 cef
!
multilink bundle-name authenticated
!
cts logging verbose
license udi pid C897VA-K9 sn FGL220992H6
!
username [removed]
!
controller VDSL 0
!
crypto isakmp policy 1
!
interface ATM0
no ip address
shutdown
no atm ilmi-keepalive
!
interface BRI0
no ip address
encapsulation hdlc
shutdown
isdn termination multidrop
!
interface Ethernet0
no ip address
shutdown
!
interface GigabitEthernet0
no ip address
!
interface GigabitEthernet1
no ip address
!
interface GigabitEthernet2
no ip address
!
interface GigabitEthernet3
no ip address
!
interface GigabitEthernet4
no ip address
!
interface GigabitEthernet5
no ip address
!
interface GigabitEthernet6
no ip address
!
interface GigabitEthernet7
no ip address
!
interface GigabitEthernet8
--> ip address 50.50.50.50 255.255.255.252
ip nat outside
ip virtual-reassembly in
duplex auto
speed auto
!
interface Vlan1
no ip address
!
interface Vlan10
ip address 192.168.1.1 255.255.255.0
ip nat inside
ip virtual-reassembly in
!
interface Vlan20
ip address 192.168.2.1 255.255.255.0
ip nat inside
ip virtual-reassembly in
!
ip forward-protocol nd
ip http server
ip http authentication local
ip http secure-server
!
--> ip route 0.0.0.0 0.0.0.0 50.50.50.49
!
ip nat inside source list 1 interface GigabitEthernet8 overload
!
access-list 1 permit 192.168.1.0 0.0.0.255
access-list 1 permit 192.168.2.0 0.0.0.255
!
control-plane
!
mgcp behavior rsip-range tgcp-only
mgcp behavior comedia-role none
mgcp behavior comedia-check-media-src disable
mgcp behavior comedia-sdp-force disable
!
mgcp profile default
!
line con 0
no modem enable
line aux 0
line vty 0 4
login
transport input none
!
scheduler allocate 20000 1000
!
end

CorporateITGuy · ‎09-22-2021

Hello,

Tried posting this in a different thread and I’m not getting any results so I am going to add it on to the end here in case someone can help me. ( here’s a link the the where I posted the question: https://community.cisco.com/t5/routing/assign-outbound-ips-and-direct-inbound-traffic/td-p/4471649 )

need to assign outbound ip addresses and direct inbound traffic.

outbound ip addresses: for example my modem is 50.50.50.50, my router is assigned 50.50.50.51, and I have webserver on 192.168.10.10 in a VLAN that I would like to assign to 50.50.50.52. This would be done with a static route correct?

Direct Inbound Traffic: for example traffic attempting to get to this webserver coming in on 50.50.50.52 on the https port (port # 443) should go to 192.168.10.10 in lets say VLAN 10. This would be another static route wouldn't it?

Thank you for any and all help!