Loop in /24 Subnet, No ping beyond .1 and .2

[BashedRoot]

Running 3650 switch. I have this odd issue where I cannot get VLAN 26 pinging on it's /24, only gateway .1 and first public IP .2

This is what I see, which doesn't look normal. How do I fix this?

The server itself is configured fine (Centos 7)

[root@localhost ~]# cat /etc/sysconfig/network-s*/ifcfg-em1
TYPE="Ethernet"
BOOTPROTO="none"
DEFROUTE="yes"
IPV4_FAILURE_FATAL="no"
IPV6INIT="yes"
IPV6_AUTOCONF="yes"
IPV6_DEFROUTE="yes"
IPV6_FAILURE_FATAL="no"
IPV6_ADDR_GEN_MODE="stable-privacy"
NAME="em1"
UUID="******"
DEVICE="em1"
ONBOOT="yes"
IPADDR="xxx.xxx.30.2"
PREFIX="24"
GATEWAY="xxx.xxx.30.1"
DNS1="8.8.8.8"
DNS2="8.8.4.4"
IPV6_PEERDNS="yes"
IPV6_PEERROUTES="yes"
IPV6_PRIVACY="no"

Cisco3650#show ip route xxx.xxx.30.0
Routing entry for xxx.xxx.30.0/24, 2 known subnets
  Attached (2 connections)
  Variably subnetted with 2 masks
C        xxx.xxx.30.0/24 is directly connected, Vlan26
L        xxx.xxx.30.1/32 is directly connected, Vlan26

Show run looks normal?

Cisco3650#show run int vlan 26
Building configuration...

Current configuration : 85 bytes
!
interface Vlan26
 description Server 26
 ip address xxx.xxx.30.1 255.255.255.0
end

[Julio E. Moisa]

Hi

That output shows a normal behavior, the /24 represents the subnet mask related to the network and the /32 represents the IP associated to the SVI.

[BashedRoot]

Doesn't sound right. I ran another check for another server (VLAN 12) on this same switch with a /22 subnet, not a /24.

Cisco3650#show run int vlan 12
Building configuration...

Current configuration : 85 bytes
!
interface Vlan12
 description Server 12
 ip address xxx.xxx.32.1 255.255.252.0
end

See, one line only.

Cisco3650#show ip route xxx.xxx.32.0
Routing entry for xxx.xxx.32.0/32, 1 known subnets
  Attached (1 connections)
L        xxx.xxx.32.1 is directly connected, Vlan12

[Julio E. Moisa]

Hi

It could be related to the network classes and their subnetted networks and masks, is that subnet a class C (192.168.x.x)?

For example:

Class B

172.17.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.17.0.0/22 is directly connected, Vlan30
L 172.17.0.1/32 is directly connected, Vlan30

This link explains the local entries:

http://www.ciscopress.com/articles/article.asp?p=2180208&seqNum=7

For example I configure the entire class B (summarized subnet) under the SVI

interface Vlan30
ip address 172.16.0.1 255.240.0.0
end

Switch#sh 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

C 172.16.0.0/12 is directly connected, Vlan30
172.16.0.0/32 is subnetted, 1 subnets
L 172.16.0.1 is directly connected, Vlan30

But If I modified it to other CIDR lowest than 12, example 9

interface Vlan30
ip address 172.16.0.1 255.128.0.0
end

it will considered as /32 if it is a subnetted network and it is not using the proper subnet mask.

Switch#sh ip route 172.16.0.0
Routing entry for 172.16.0.0/32, 1 known subnets
Attached (1 connections)
L 172.16.0.1 is directly connected, Vlan30

The private classes are:

10.0.0.0/8
172.16.0.0/12
192.168.0.0/16

[BashedRoot]

/24 = C class with a 255.255.255.0 subnet mask.

My settings are right, but IPs are not pinging. I think something is wrong with the VLAN26 itself. VLAN12 does not have the 2 (C and L) lines, just one and it has a /22 subnet.

Furthermore, I even tried modifying VLAN26 to have a /29 prefix primary and /24 subnet secondary. This always works on other servers I have with Centos, same switch too.

Even the /29 did not work except on gateway and primary .50 IP. .51 and rest did not ping either. Something is up with the actual VLAN I think.

[BashedRoot]

Would appreciate help to get this strange issue resolved. I know for a fact I set up the IP assignment on the VLAN and the server's network config in Centos Linux itself. But, there's still a hiccup I believe on the VLAN side.

[dperezoquendo]

Hello,

I'm going to backtrack a bit if you don't mind.

1. You have the following configured:

vlan 26

int vlan 26

  ip address xxx.55.30.1 255.255.255.0

2. The server connecting to g0/21 (a vlan 26 access port) is configured to use an ip within the xxx.55.30.0/24 subnet. For example, xxx.55.30.2 255.255.255.0

Even with above setup, you cannot ping xxx.55.30.1, is this correct?

[BashedRoot]

> Even with above setup, you cannot ping xxx.55.30.1, is this correct?

Wrong, as I stated a few times, I can ping .1 gateway and .2 public IP, but cannot ping the remainder on the /24 subnet.

[Jon Marshall]

And this remainder of the subnet is simply allocated to the server with the .2 IP address, is that correct ?

If so until you can describe how the server handles these IPs I'm not sure how we can help because it does not seem to be an issue with the switch ie. you can ping the SVI on the switch.

Jon

[dperezoquendo]

I see, I apologize for that. There's a lot of information to go through on this forum and I have some difficulties in fully understanding what all has happened.

I was wondering what you exactly mean by public IP. Where does this switch sit in your topology? E.g. LAN, DMZ, WAN? And what does IP xxx.55.30.2 belong to? Is this the server IP itself? Actually, what is the last octect of the server ip?

Generally when I see "public IP", I imagine a NATed IP address. In my opinion, you shouldn't be using a public IP block internally on your network.

Also, where does the remainder of the /24 subnet sit in your network? From your earlier results "show ip route xxx.xxx.30.0", I noticed you had 0 routes for other devices. If they were on the same switch, they should be able hit since you can reach default gateway. However, if they aren't on the same switch, you will need to:

1. Verify you're trunking configurations

2. Verify the other switches have vlan26 configured

3. Verify that access ports are configured for vlan26 on the other switches

4. Verify your routing via static routes or a dynamic protocol

Hope some of this helps and I apologize again if I'm repeating things that have already been checked.

[paul driver]

Hello

So just confirm - you did or didn't try a different host other than this server and connect it to the switches  and test?

As stated if the switch was the problem then I'd expect ever other server have the same problem 

The switch config looks okay-cannot comment on your server hence why a suggested device change maybe with a laptop or pc twith correct assigned IP address -subnet- default gateway and post the test results

res

Paul

[BashedRoot]

Once again:

Cisco3650#show run int Gi1/0/21
Building configuration...

Current configuration : 282 bytes
!
interface GigabitEthernet1/0/21
 description Server 26
 switchport access vlan 26
 switchport trunk allowed vlan 3,5,8,17-19,26,39,43,50,51,70,74,76,78,84,97-99
 switchport trunk allowed vlan add 101-103,108,110,112,119,500,600,611,612,950
 switchport mode access
 speed 100
end



Cisco3650#show run int vlan 26 
Building configuration...

Current configuration : 85 bytes
!
interface Vlan26
 description Server 26
 ip address xxx.55.30.1 255.255.255.0
end



Gi1/0/21  Server 26          connected    26         a-full    100 10/100/1000BaseTX

[paul driver]

Hello

Can you try attaching host pc instead of your server to an access port on either switch for any of the 4 vlans your having issues with, Assign this host addressing and see if you can reach the other vlans

This will tell either way if its the switch or the server causing this

res
Paul

[paul driver]

Hello

Running 3650 switch. I have this odd issue where I cannot get VLAN 26 pinging on it's /24, only gateway .1 and first public IP .2

Do you mean by this you cannot ping other vlans?
Can you ping between vlans?
Do you have ip routing enabled?
Do you have the SVI ip address for 26 configured anywhere else?
Have you created the L2 vlan for this vlan?
What does the arp table show for your server
Have you tested another device other than your server on this vlan?


res
Paul

[BashedRoot]

This issue is solely VLAN26. All other VLANs work fine and ping fine. Why would I need to create an L2 VLAN for the VLAN? I'm not understanding. My simple standard step is "vlan #", assign IPs and port and that's it. It works just like the 20+ others working now.

> Do you have the SVI ip address for 26 configured anywhere else?

How/where do I check that?

> Do you have ip routing enabled?

Not sure what you mean, all other VLANs work fine on the switch so the answer is yes.