Cisco ASA TCP Syslog Problem

I ran today into a big problem with configuring an TCP syslog server on an Cisco ASA.

logging host "interface_name" "server_ip" tcp/514

After I put in the configuration and someone from the server administration restarted the syslog server and suddenly the whole communication through the ASA stopped working completely.

I saw the following messages in the ADSM and quickly realised that this could be only caused by the TCP logging configuration.

%ASA-3-201008: Disallowing new connections

I didn’t looked before if the feature is disabled to block new connections when a TCP-connected syslog server is down. This is very important that you disable the feature before you configure TCP syslog servers otherwise you ran into the same problem like me.

Here the command to disable the feature:

logging permit-hostdown

In my case I just forgot to check before and will definitively remember for the next time ūüėČ

First Hop Redundancy Configuration

The redundancy of the default gateway is important to keep network communication running in an case of an failure. I just want to show what choices you have there and how to configure these on a Cisco switch.

HSRP РHot standby router protocol is standardized but licensed by Cisco Systems and very similar to the next one VRRP.

VRRP РVirtual router redundancy protocol is open standard and an alternative to Cisco HSRP both providing the same functionality. If you have network equipment from different vendors or want to keep open standard then use VRRP.

GLBP РGateway load balancing protocol is Cisco proprietary and supports load balancing like the name already says.

HSRP configuration:

interface GigabitEthernet0/0
 ip address
 standby version {1 | 2}
 standby 1 ip
 standby 1 timers *hello* *dead*
 standby 1 priority *priority*
 standby 1 preempt
 standby 1 authentication md5 key-string *password*
 standby 1 track *interface* *value*
 standby 1 track *object* decrement *value*

Show command:

show standby brief

VRRP configuration:

interface GigabitEthernet0/0
 ip address
 vrrp 1 ip
 vrrp 1 timers {advertise *hello* | learn}
 vrrp 1 priority *priority*
 vrrp 1 preempt
 vrrp 1 authentication md5 key-string *password*
 vrrp 1 track *object* decrement *value*

Show command:

show vrrp brief

GLBP configuration:

interface GigabitEthernet0/0
 ip address
 glbp 1 ip
 glbp 1 timers *hello* *dead*
 glbp 1 timers redirect *redirect* *time-out*
 glbp 1 priority *priority*
 glbp 1 preempt
 glbp 1 forwarder preempt
 glbp 1 authentication md5 key-string *password*
 glbp 1 load-balancing *method*
 glbp 1 weighting *weight* lower *lower* upper *upper*
 glbp 1 weighting track *object* decrement *value*

Show command:

show glbp brief

The configuration can be also done on an SVI (VLAN) interface. You don’t need to configure everything, if you don”t set the timers to an custom value the default is taken same like with priority but if you change the timers you need to configure them both sides otherwise it will not work.

If you want to know more have a look at the Cisco First Hop Redundancy Protocols Configuration Guide

How correct network cabling should look like!

Network cabling in a data centre should not look like in the following picture ūüėČ there you have no¬†structure¬†and makes it difficult for someone else to look through how every server is connected.

To make your life and work easier you just need to think before about what colors you use and then create an cabling standard what you always follow. Basically I choose three colors: blue, red and yellow. Yellow is management traffic, blue and red are main network connections (ports on the server must be teamed to have a redundant connectivity).

Here you clearly see that every server has an redundant connection to one of the switches in the rack. The blue cables are always connected to the top switch in the rack and the red to the second switch.

Here how the complete rack looks like, always look to keep it organised and follow your cabling standard.


Cisco IP SLA Configuration

Not everyone knows how powerful the Cisco IP SLA feature is and here an short example what you can do with it.

At first you need to create the monitor in my case I just want to do basic ICMP testings to a specific IP address, you can of course also create other IP SLA operations in the end it just depends for what you need the IP SLA feature.

ip sla monitor 1
 type echo protocol ipIcmpEcho source-interface FastEthernet1/0
 timeout 300
 frequency 3

Then you need to start the IP SLA monitor

ip sla monitor schedule 1 life forever start-time now

With the show command you can look if the tests are successful and then continue with the next step

show ip sla monitor statistics

Here you create the track definition

track 1 rtr 1 reachability

In the end you just need to add the track condition, in my example an static default route

ip route track 1

When the IP is reachable the static route is within the routing table of the Cisco router, when the IP is unreachable IP SLA deletes the static route from the routing table. I mostly use IP SLA to failover to an back-up internet connection because its very easy to configure.

More information you can find in the Cisco IOS IP SLAs Configuration Guide

GNS3 Network Simulator

Found something really cool today ūüôā

GNS3 is a graphical network simulator where you can set-up complex virtual networks and run Cisco and Juniper routers or switches. The best is that you can also integrate Qemu and Virtualbox into your virtual lab environment what I really love. You can easily test new configurations on devices without having to set-up all these in hardware.

The only little problem is that you need a quite power system¬†to do all of that. Otherwise I tested GNS3 on an 3 year old laptop with Intel Core2Duo and 4 GB RAM and run up to 6 Cisco routers without any big problems what’s enough for me at the moment.

Ah I forgot, you can of course also use Wireshark to capture packets on an link between two devices.

Here the link to the website: