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I am Val Glinskiy, network engineer specializing in data center networks. TIME magazine selected me as Person of the Year in 2006.

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Wednesday, October 14, 2009

How to generate lots of BGP routes

I needed to test in the lab whether my Cisco router can handle more than 300K routes - size of current full BGP table. Now, Cisco router can only accept 200 network statements under router bgp configuration, so I would need 1500 routers. Even if I had that many routers to my disposal, it would have taken days to configure all of them. As always, open source software can help. Quagga lets you run OSPF, BGP, RIP, RIPng on Linux and Solaris. If you go with all default options, it is very easy to install. Download and unpack. Go to quagga directory, in my case it was quagga-0.98.6, type
./configure
make
sudo make install
That's it. By default, it went into /usr/local/. I have Debian 4 (Etch) with 2.6.8 kernel and a lot of development packages installed. The only thing I had to do was to add /usr/local/lib to /etc/ld.so.conf file and run /sbin/ldconfig.
Here is the setup


Now I need a valid configuration file for Quagga BGP. Adding 300000 network statements manually is not something system administrators do on Linux. Hence, here is the script
#!/usr/bin/perl

my $host="quagga-host";         #quagga router name
my $logpass="zebra";            #login password
my $enable="zebra";             #enable password
my $myasn="65099";              #local AS number
my $router_id="172.31.2.2";     #bgp router-id
my $remote_as="65001";          #remote-as number
my $remote_ip="172.31.2.1";     #BGP neighbor ip address
my $route_count=0;
my $max_routes=300000;              #max number of routers to generate

open (BGPCONF,'>bgpd.conf')|| die "Can not open bgpd.conf for writing";
print BGPCONF "hostname $host\npassword $logpass\nenable password $enable\nline vty \n";
print BGPCONF "router bgp $myasn\n  bgp router-id $router_id\n  neighbor $remote_ip remote-as $remote_as\n";
MAXR: while ($route_count <= $max_routes ) { 
$octet1=int(rand(223))+1; #generate 1st octet randomly in 1-223 range, 224 and up is multicust and class E  
if ($octet1 ==127) {next;} #need to make sure that 127.X.X.0/24 is excluded 
$octet2=0;  
while ( $octet2 <= 255 ){
$octet3=0;
while ( $octet3 <= 255 ) {
print BGPCONF "  network $octet1\.$octet2\.$octet3\.0/24\n";
$octet3++;
$route_count++;
if ($route_count == $max_routes) {last MAXR;}
}
$octet2++;
}
}
close BGPCONF;
this script will generate bgpd.conf for Quagga. Since it is lab environment not connected to any real network, I do not really care about zebra configuration or restricting access to Quagga BGP console. Copy bgpd.conf file into /usr/local/etc and run /usr/local/sbin/bgpd -d -f /usr/local/etc/bgpd.conf -u root -g root Again, this is not production environment. Do not run Quagga as root in production. Here is relevant configuration from Cisco router:
interface GigabitEthernet0/0
ip address 172.31.2.1 255.255.255.0
network 172.31.2.0 mask 255.255.255.0
media-type rj45
negotiation auto
!
router bgp 65001
no synchronization
bgp log-neighbor-changes
neighbor 172.31.2.2 remote-as 65099
no auto-summary
!
Let's see if it works. On Linux host:
sh-2.05b$ telnet localhost 2605
Trying 127.0.0.1...
Connected to localhost.localdomain.
Escape character is '^]'.

Hello, this is Quagga (version 0.98.6).
Copyright 1996-2005 Kunihiro Ishiguro, et al.


User Access Verification

Password:
quagga-host> sho ip bgp summ
BGP router identifier 172.31.2.2, local AS number 65099
2 BGP AS-PATH entries
0 BGP community entries

Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
172.31.2.1      4 65001     283     606        0    0    0 03:41:55        1

Total number of neighbors 1
quagga-host>
on Cisco:
R1#sho ip bgp sum
BGP router identifier 192.0.2.2, local AS number 65001
BGP table version is 330002, main routing table version 330002
310001 network entries using 40920132 bytes of memory
310001 path entries using 16120052 bytes of memory
3/2 BGP path/bestpath attribute entries using 444 bytes of memory
1 BGP AS-PATH entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
Bitfield cache entries: current 1 (at peak 2) using 32 bytes of memory
BGP using 57040684 total bytes of memory
BGP activity 310001/0 prefixes, 320001/10000 paths, scan interval 60 secs

Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
172.31.2.2      4 65099     602     322   330002    0    0 03:38:59   310000
Yep. It works.

Friday, October 09, 2009

BGP and BFD (Bidirectional Forwading Detection)

If you have Ethernet uplink to your ISP, the chances are high that it looks like this:



The Layer2 device could be "on the wire" provider or Ethernet over MPLS service. The problem arises when, for example, connection between Layer2 device and ISP router goes down



The BGP session with R1 on ISP router will reset immediately, unless you configured "no bgp fast-external-fallover". But R1 will rely on BGP hello messages to detect if neighbor still alive. It might take R1 up to 3 minutes detect that ISP is not available and for these 3 minutes R1 will be sending traffic to black hole instead of re-converging and sending traffic to your backup link. You have backup link, don't you?
Here are the syslog messages from R1 and ISP routers. To imitate link failure I shutdown interface on ISP

router ISP:
Oct 9 17:55:18 UTC: %LINK-5-CHANGED: Interface GigabitEthernet2/5, changed state to administratively down
Oct 9 17:55:18 UTC: %BGP-5-ADJCHANGE: neighbor 172.31.255.1 Down Interface flap


router R1:
Oct 9 17:57:24 UTC: %BGP-5-ADJCHANGE: neighbor 172.31.255.2 Down BGP Notification sent
Oct 9 17:57:24 UTC: %BGP-3-NOTIFICATION: sent to neighbor 172.31.255.2 4/0 (hold time expired) 0 bytes

Note the timestamps of first and last messages. That's not good, especially if every minute of downtime costs you a bundle. You can adjust bgp timers, but lowest you can go is 1 second and it could be hard on CPU.
BFD protocol allows you to go to microseconds level. It is very lightweight and easy to configure.
On interfaces facing Layer2 device apply command:

bfd interval 100 min_rx 100 multiplier 3
To check if BFD is configured properly:
#sho bfd neighbor

OurAddr NeighAddr LD/RD RH/RS Holddown(mult) State Int
172.31.255.2 172.31.255.1 3/7 Up 0 (3 ) Up Gi2/5

under "router bgp" configuration:

neighbor [neighbor IP] fall-over bfd

Now let's imitate link failure again. Shutdown interface on router ISP:

Oct 9 18:14:27.408 UTC: %LINK-5-CHANGED: Interface GigabitEthernet2/5, changed state to administratively down
Oct 9 18:14:27.408 UTC: %BGP-5-ADJCHANGE: neighbor 172.31.255.1 Down Interface flap


On R1

Oct 9 18:14:27.673 UTC: %BGP-5-ADJCHANGE: neighbor 172.31.255.2 Down BFD adjacency down


The difference now in milliseconds. The hard part is to convince your ISP to configure BFD on their side.
At this moment Cisco supports BFD on Ethernet interfaces only and only for directly connected BGP peers, i.e. no multi-hop BGP.
BFD requires UDP ports 3784 and 3785 to be open in case you have ACL applied to your uplink interface.

Tuesday, October 06, 2009

CCIE R&S v4.0

I just attended webcast about new CCIE R&S written and lab exam. It looks like MPLS portion of the exam is going to be much easier than 642-611 exam which is required for CCIP certification.

Wednesday, September 16, 2009

bpduguard vs. bpdufilter

Suppose you have a switch with servers connected to it. It's called "access layer switch" in Cisco lingo. There is no need to go through all spannig-tree states on these host-facing ports. So, you make port transition faster to forwarding mode with "switchport portfast" interface command. One of the benefits is that if your server boots fast, it does not need to wait until port finishes going through all STP port states and can start transmitting data immediately.
Since servers normally should ignore BPDUs coming from a switch, there is no need to send them to a server in the first place. To filter out outgoing BPDUs apply interface command "spanning-tree bpdufilter enable".
But when BPDU is received on the port with bpdufilter enabled, the port's portfast status is disabled and port will participate in spanning-tree.
 At all times network needs to be protected from unauthorized device that might decide to participate in your spanning-tree topology and cause spanning-tree loop or try to hijack STP root. Interface command "spanning-tree bpduguard enable" puts interface in err-disable mode whenever BPDU is received from connected device.
What will happen if you have both bpdufilter and bpduguard enabled on the interface?

spanning-tree portfast
spanning-tree bpdufilter enable
spanning-tree bpduguard enable
bpdufilter takes precedence and bpdugard does not work. Although bpduguard needs more administrative overhead - port needs to be enabled manually - it makes your network more secure.

Monday, August 17, 2009

Cisco router as Frame-Relay switch

There are a lot of examples on the 'Net how to configure Cisco router to act as Frame Relay switch. All of them use command "frame-relay route". Here is (one more) example





For the topology on the picture above, the configuration would look like this

interface Serial2/0
no ip address
encapsulation frame-relay
no fair-queue
clock rate 128000
frame-relay intf-type dce
frame-relay route 103 interface Serial2/2 301
!
interface Serial2/2
no ip address
encapsulation frame-relay
clock rate 128000
frame-relay intf-type dce
frame-relay route 301 interface Serial2/0 103
end
Here is another way to configure:
interface Serial2/0
no ip address
encapsulation frame-relay
no fair-queue
clock rate 128000
frame-relay intf-type dce
!
interface Serial2/2
no ip address
encapsulation frame-relay
clock rate 128000
frame-relay intf-type dce
!
connect mylink Serial2/0 103 Serial2/2 301

In latter case I used command "connect". Unlike "frame-relay route", "connect" command can be used only once for each pair of DLCIs that need to be able to talk to each other. If you need to have many Frame Relay links, using "connect" is less error-prone and configuration is easier to read.
To see connection status:

#show connection all

ID Name Segment 1 Segment 2 State
========================================
2 mylink Se2/0 103 Se2/2 301 UP

Monday, July 20, 2009

Need to find out Cisco switch serial number?

Yes, you can do it by logging in and running "show idprom backplane" or "show inventory". What if you have hundreds of switches and need to update your inventory list. Going to every switch, typing commands and writing down serial numbers is very time consuming. There is also Expect script, but I am not a big fan of putting clear text passwords into code. So, my favorite SNMP to the rescue.
Serial number OID for modular switches (4500 and 6500) is .1.3.6.1.2.1.47.1.1.1.1.11.1. For Catalyst 2960 and 3500: 1.3.6.1.2.1.47.1.1.1.1.11.1001

Here is the quick shell script to get serial number and location of each switch.

for i in `cat switches.txt`
do
serial=`snmpwalk -Ov -Oq -v2c -c public $i 1.3.6.1.2.1.47.1.1.1.1.11.1001`
location=`snmpwalk -Ov -Oq -v2c -c public $i system.sysLocation`
echo -e "$i \t $serial \t $location"
done

File switches.txt contains ip addresses of my access switches, one per line. It goes without saying that each switch must have "snmp-server location" configured.

Monday, June 22, 2009

JUNOS as a second language

Juniper was kind enough to post "JUNOS As A Second Language" e-learning course aimed at network administrators familiar with Cisco IOS. As somebody who works in production environment I could not help but notice how easy it is to revert changes in JUNOS with "commit confirmed" command.
Well, it turns out that IOS 12.4 has similar feature with "configure replace". From Cisco documentation:

Configuration Rollback Confirmed Change

The Configuration Rollback Confirmed Change feature enables an added criteria of a confirmation to configuration changes. This functionality enables a rollback to occur if a confirmation of the requested changes is not received in a configured time frame. Command failures can also be configured to trigger a configuration rollback.

The following steps outline how this process is achieved:

1. When entering configuration mode, this new option allows you to request confirmation (a confirmation time limit must be supplied) of the configuration changes.

2. After exiting configuration mode, you must enter the confirmation command. If no confirmation is entered within the requested time limit, the configuration will revert to its previous state.


configure replace target-url [nolock] [list] [force] [ignorecase] [revert trigger [error] [timer minutes] | time minutes]

It might come in handy next time when you change IP address on the wrong interface or make mistake in ACL.
Disclaimer: I strongly advise that you have console server with out-of-band access connected to all your critical production routers.

Friday, June 19, 2009

Last Error: PCALC:: No addresses to connect

Ever since I passed "Implementing Cisco MPLS" (642-611) exam, I've been aching to try my hands at MPLS TE. So, here is the task:





Click on image to see bigger version.

Since R2-R4 link is T3, OSPF will pick R2-R3-R5 path from R1 to either R6 or R7 leaving R2-R4-R5 link underutilized. At the same time I know that traffic from R1 to 10.0.0.0/24 is going to low enough to fit comfortably into T3 link. I wanted to create explicit path tunnel R1-R2-R4-R5-R7 with backup dynamic tunnel. I am going to skip configuration part - there are more then enough examples on the 'Net.
Let's see if tunnel is up
R1#sho mpls traffic-eng tunnels

Name: 6503sw2_t0 (Tunnel0) Destination: 192.168.1.4
Status:
Admin: up
Oper: down Path: not valid Signalling: Down path option 1, type explicit mypath

Config Parameters:
Bandwidth: 0 kbps (Global) Priority: 7 7 Affinity: 0x0/0xFFFF
Metric Type: TE (default)
AutoRoute: enabled LockDown: disabled Loadshare: 0 bw-based
auto-bw: disabled

History:
Tunnel:
Time since created: 20 hours, 1 minutes
Time since path change: 3 minutes, 24 seconds
Number of LSP IDs (Tun_Instances) used: 334
Prior LSP:
ID: path option 1 [309]
Removal Trigger: path option removed
Last Error: PCALC:: No addresses to connect 172.16.0.14 to 172.16.0.10
Not good. Searching for this type of error message gives one sage advise:
For cases involving an explicit path option, you can try to narrow down the problem by first checking every hop in the explicit hop list. You can also try to back down the tunnel: Move the tail one hop back each time to see if the tunnel comes up. If the tunnel comes up when you move the tail to a previous hop, you can conclude that there is a problem between that hop and the next hop, and you can start scrutinizing that hop carefully.
And so I did. Let's see how R2 and R5 see R4:


R2# show ip rsvp neighbor
Neighbor Encapsulation Time since msg rcvd/sent
172.16.0.18 Raw IP 00:02:12 00:02:10
172.16.0.21 Raw IP 00:02:10 00:02:23




R5#show ip rsvp neighbor
Neighbor Encapsulation Time since msg rcvd/sent
172.16.0.1 Raw IP 00:03:59 00:04:18
172.16.0.6 Raw IP 00:04:16 00:03:59
Hmm, they do not see R4 as RSVP neighbor at all. What's going on on R4?

R4# sho ip rsvp interface detail gi 0/0
Gi0/0:
Interface State: Up
Bandwidth:
Curr allocated: 0 bits/sec
Max. allowed (total): 30M bits/sec
Max. allowed (per flow): 30M bits/sec
Max. allowed for LSP tunnels using sub-pools: 0 bits/sec
Set aside by policy (total): 0 bits/sec
Admission Control:
Header Compression methods supported:
rtp (36 bytes-saved), udp (20 bytes-saved)
Traffic Control:
RSVP Data Packet Classification is ON
Signalling:
DSCP value used in RSVP msgs: 0x3F
Number of refresh intervals to enforce blockade state: 4
Number of missed refresh messages: 4
Refresh interval: 30
Authentication: disabled
How does it compare with R4-facing interface on R5?


R5#sho ip rsvp interface detail gi 0/2

Gi0/2:
RSVP: Enabled
Interface State: Up
Bandwidth:
Curr allocated: 0 bits/sec
Max. allowed (total): 40M bits/sec
Max. allowed (per flow): 40M bits/sec
Max. allowed for LSP tunnels using sub-pools: 0 bits/sec
Set aside by policy (total): 0 bits/sec
Admission Control:
Header Compression methods supported:
rtp (36 bytes-saved), udp (20 bytes-saved)
Traffic Control:
RSVP Data Packet Classification is ON via CEF callbacks
Signalling:
DSCP value used in RSVP msgs: 0x3F
Number of refresh intervals to enforce blockade state: 4
Authentication: disabled
Key chain:
Type: md5
Window size: 1
Challenge: disabled
Hello Extension:
State: Disabled
"RSVP: Enabled" string is missing in R4 command output. After some research I found that I need "T" type IOS to run RSVP-TE on R4 which is Cisco 3825.
Let's see what we have after the upgrade:

R4#sho ip rsvp interface detail gi 0/0

Gi0/0:
RSVP: Enabled
Interface State: Up
Bandwidth:
Curr allocated: 5M bits/sec
Max. allowed (total): 30M bits/sec
Max. allowed (per flow): 30M bits/sec
Max. allowed for LSP tunnels using sub-pools: 0 bits/sec
Set aside by policy (total): 0 bits/sec
Admission Control:
Header Compression methods supported:
rtp (36 bytes-saved), udp (20 bytes-saved)
Traffic Control:
RSVP Data Packet Classification is ON
Signalling:
DSCP value used in RSVP msgs: 0x3F
Number of refresh intervals to enforce blockade state: 4
Authentication: disabled
Key chain:
Type: md5
Window size: 1
Challenge: disabled
Hello Extension:
State: Disabled
and tunnel:

R1#sho mpls traffic-eng tunnels bri
Signalling Summary:
LSP Tunnels Process: running
Passive LSP Listener: running
RSVP Process: running
Forwarding: enabled
Periodic reoptimization: every 3600 seconds, next in 3042 seconds
Periodic FRR Promotion: Not Running
Periodic auto-bw collection: every 300 seconds, next in 42 seconds
TUNNEL NAME DESTINATION UP IF DOWN IF STATE/PROT
6503sw2_t0 192.168.1.4 - Gi2/1 up/up
Much better. Confirm routing

R1#sho ip route 10.0.0.0 255.255.255.0
Routing entry for 10.0.0.0/24
Known via "ospf 100", distance 110, metric 14, type intra area
Last update from 192.168.1.4 on Tunnel0, 19:41:13 ago
Routing Descriptor Blocks:
* 192.168.1.4, from 192.168.1.4, 19:41:13 ago, via Tunnel0
Route metric is 14, traffic share count is 1
Now, since MPLS TE tunnel is unidirectional, I need to create R7-R5-R4-R2-R1 tunnel as well.

Thursday, May 21, 2009

CCIP accomplished

Yesterday I passed "Implementing Cisco MPLS" (642-611) exam. That was last one for me to complete CCIP certification process. I want to share my "CCIP reading list":


Routing TCP/IP, Volume 1 (2nd Edition)(CCIE Professional Development)






Routing TCP/IP, Volume II (CCIE Professional Development)








BGP Design and Implementation






Cisco QOS Exam Certification Guide (IP Telephony Self-Study) (2nd Edition)






MPLS Fundamentals







The list is not exclusive. In addition to that I used Cisco's command reference guide and IOS documentation on Cisco's website and built small lab to practice. I also tried using exam simulators like RealExams, a.k.a. Pass4Sure, a.k.a. TestKing. Actually, I am not sure if it is the same company or they steal from each other, but simulators' content is almost identical and I found all of them to be waste of money - ridden with errors and outdated. For 642-611 exam, I tried Bosons Software simulator. This one was of much better quality, but turned out to be too easy to be a good help for MPLS exam preparation. Even if you manage to achieve 80-90% accuracy in this simulator, your real exam score won't be high enough to pass.

Tuesday, May 05, 2009

2 more Netscreen's OIDs

1.3.6.1.4.1.3224.4.1.1.1.27.X shows what Netscreen thinks latency (in ms) is through IPSec tunnel number X. See my old post on how to find tunnel number.

Here is another one. How much data was transferred via policy number Y.

1.3.6.1.4.1.3224.10.2.1.6.Y.0
Beware, it reports in Bytes/sec. In order to make it work, you'll have to configure policy with "count" option.

Thursday, March 19, 2009

3 down, 1 more to go

Yesterday I passed "Implementing Cisco QoS" exam 642-642. I need to pass 642-611 "Implementing Cisco MPLS" to complete CCIP certification.

Tuesday, March 10, 2009

Tracking routing entries on Cisco7600 via SNMP

I have Cisco7604 with SUP720 running c7600rsp72043-ipservicesk9-mz.122-33.SRD.bin. Cisco's SNMP object navigator claims that this image supports RFC1213-MIB which has ipRouteTable. In reality here is what I got

~$ snmpwalk -v2c -c public [myrouter] ipRouteDest
RFC1213-MIB::ipRouteDest = No Such Object available on this agent at this OID


After "Asking" around, I found RFC2096, that states:

The ipForwardTable updates the RFC 1213 ipRouteTable to display multipath IP Routes. This is in turn obsoleted by the ipCidrRouteTable.

The ipCidrRouteTable updates the RFC 1213 ipRouteTable to display multipath IP Routes having the same network number but differing network masks.


ipCidrRouteTable is actually supported by my IOS image, even though Cisco's SNMP object navigator declares it "depricated" and recommends using inetCidrRouteTable (1.3.6.1.2.1.4.24.7)

~$ snmpwalk -v2c -c public [myrouter] inetCidrRouteTable
IP-FORWARD-MIB::inetCidrRouteTable = No Such Object available on this agent at this OID


No luck again, but ipCidrRouteTable (numeric 1.3.6.1.2.1.4.24.4) works just fine.

Here is the list of the objects in ipCidrRouteTable
ipCidrRouteTable 1.3.6.1.2.1.4.24.4
ipCidrRouteEntry 1.3.6.1.2.1.4.24.4.1
ipCidrRouteDest 1.3.6.1.2.1.4.24.4.1.1
ipCidrRouteNextHopAS 1.3.6.1.2.1.4.24.4.1.10
ipCidrRouteMetric1 1.3.6.1.2.1.4.24.4.1.11
ipCidrRouteMetric2 1.3.6.1.2.1.4.24.4.1.12
ipCidrRouteMetric3 1.3.6.1.2.1.4.24.4.1.13
ipCidrRouteMetric4 1.3.6.1.2.1.4.24.4.1.14
ipCidrRouteMetric5 1.3.6.1.2.1.4.24.4.1.15
ipCidrRouteStatus 1.3.6.1.2.1.4.24.4.1.16
ipCidrRouteMask 1.3.6.1.2.1.4.24.4.1.2
ipCidrRouteTos 1.3.6.1.2.1.4.24.4.1.3
ipCidrRouteNextHop 1.3.6.1.2.1.4.24.4.1.4
ipCidrRouteIfIndex 1.3.6.1.2.1.4.24.4.1.5
ipCidrRouteType 1.3.6.1.2.1.4.24.4.1.6
ipCidrRouteProto 1.3.6.1.2.1.4.24.4.1.7
ipCidrRouteAge 1.3.6.1.2.1.4.24.4.1.8
ipCidrRouteInfo 1.3.6.1.2.1.4.24.4.1.9

If you run BGP and accept all routes from the internet, it might be useful to watch the size of your routing table. ipCidrRouteNumber (1.3.6.1.2.1.4.24.3)does just that. If you want to graph it in Cacti use 1.3.6.1.2.1.4.24.3.0 For some reason Cacti needs .0 in the end

Wednesday, February 25, 2009

Friday, February 13, 2009

Connect F5 LTM/GTM to Perle IOLAN console server

I personally prefer Cyclades (now part of Avocent) console servers since they run Linux and I can use vi to edit configuration files. The only problem is that Cyclade's console servers come with only one Ethernet port. What if a switch to which Cyclade console server is connected via Ethernet dies and you need to access its console to figure out what is going on? You can always hook up modem to you console server and dial in, but in this case only one person can connect and with proliferation of VoIP analog phone lines in offices are getting hard to come by.
So, after some search I found Perle's IOLAN console server which have 2 Ethernet ports. These ports can be used in Active/Standby configuration, meaning you can assign 1 IP address and when 1st Ethernet port goes down, IOLAN moves this IP address automatically to second port. For this feature alone I am willing to tolerate their Windows configuration client software.

Now I need to connect IOLAN to F5 LTM/GTM console. Since LTM's console is DB9 male connector and IOLAN is RJ45, I need RJ45-DB9 female converter. I buy these converters at pccables.com. The wires in that converter on RJ45 side are connected like this:
1 Blue
2 Orange
3 Black
4 Red
5 Green
6 Yellow
7 Brown
8 White

I need to plug those wires into DB9 side of the converter like this

RJ45 DB9
Blue 6
Orange 8
Black 4
Red 2
Green 3
Yellow 5
Brown 7
White 1

Now, take regular straight network cable, plug one end into RJ45-DB9 converter, another into IOLAN port. Done. Do not forget that by default IOLAN's port speed is 9600 and F5's is 19200.

Wednesday, February 04, 2009

Packetization Layer Path MTU Discovery

A lot of network administrators block all ICMP traffic on the network's edge. Although some ICMP packets can be used in DDoS, ICMP type 3 plays important role in Paht MTU discovery. If ICMP is completely blocked, sending side can not reliably determine MTU and that can lead to re-transmissions and slower data transfer. Sometimes, ICMP blocking network could be outside your control, so you can not change ACL or firewall rules. In this case Packetization Layer Path MTU Discovery can be used. It utilizes TCP for maximum packet size discovery (RFC4821). To enable PLPMTUD on Linux:
echo 2 > /proc/sys/net/ipv4/tcp_mtu_probing
or
in /etc/sysctl.conf net.ipv4.tcp_mtu_probing = 2