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Category Archives for "Networking"

Hitting the PF state table limit

I recently had an issue with an OpenBSD firewall where the number of state table entries was hitting the default limit of 10,000. When this limit is reached, no new state entries can be created. If you're using “keep state”, “modulate state” or “synproxy state” on your rules or if you're running OpenBSD 4.1 or newer (where “keep state” is the default on all rules) this could mean that:

  • You cannot make new connections through the firewall
  • You cannot make new connections to the firewall
  • You cannot make new connections from the firewall

So…. if you hit the state table limit it's kinda bad, mmmkay?

ZFS File Server

Specifications Total storage raw: 10TB Total storage usable: 5TB Case Norco RPC-4220 - 20 hot-swap bay, 4RU chassis PSU Corsair HX 750W Motherboard Supermicro X8STE - single socket 1366; 2x Intel 82574L GigE NIC; Matrox G200 GPU CPU Intel Xeon E5620 Westmere 2.4GHz Quad Core RAM 24GB (6x4GB) Kingston 240-pin DDR SDRAM ECC Unbuffered Controller Cards Intel SASWT4I (LSI SAS1064E chipset) PCIe x4 4-port SAS HBA LSI 9201-16i 6GB/s PCIe 2.

Website Redesign

If you've visited this site before then it's obvious to you the site has undergone a major face lift. All of the content that was on the old site is still here, it's just at a different URL. Some of the more popular pages on the site are now here: Juniper Networks Olive Monitoring BIND9 Monitoring Postfix NetPacket PERL modules for IPv6 and OpenBSD packet filter OpenBSD SNMP MIBs As these pages are updated or when I add new tools or scripts, I plan on posting a blog entry to that affect.

Troubleshooting OSPFv2 Neighbors (Part2)

This will seem very similar to t he last post, again going on simple. Things that can be overlooked if one is not careful, doesn’t look at everything with a magnifying glass, and becomes over...

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IPv6 Tutorial: The overview

I will start from the beginning; two weeks ago I wrote a post claiming that IPv4 is depleting and IPv6 is coming soon; and since we are considering deploying IPv6 soon in our network, I thought it might be useful to write about IPv6 migration and transition strategies. Although, this is important but I think [...] No related posts. Related posts brought to you by Yet Another Related Posts Plugin.

vPC and VSS features and Comparison

Seems like other than IPv6 allot of the talk lately (in the Datacenter anyways) is about MEC, or multi-chassis etherchannel. Using something like this in the aggregation part of the Datacenter not...

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How Network Operators can cooperate: the NLNOG RING

In December 2010 I started a project with a few friends to make life for network engineers in the Netherlands better.

I noticed that there are a lot of friendly 'shell access' exchange deals between dutch network operators. This makes it easier for parties to debug network issues and troubleshoot from the outside. A point of view outside your network is absolutely essential, seeing what others see is a useful thing for a variety of network problems. Well known examples are "it works for even numbered ip address, but not for odd numbered ip address via this and this route".

The NLNOG RING tries to do this in a more organized way, basically the deal is "donate 1 machine, and gain access to all other machines in the ring". So far already 10 organisations are participating.

How useful is the ring exactly? A very nice example is executing a traceroute from ten different autonomous systems: nlnog ring example.

More information about the NLNOG RING can be found on the website we've launched today: ring.nlnog.net.

Ticket #16 – Repubished

Next ticket, Ticket 17, which will be about IGP and EEM will be published on CCIEFlyer.com, then it will be republished here again. ... • R1 is configured with redundant bidirectional connection between R3 and R4's Lo0. ... • R1 is using NAT to allow connectivity, exposing R3 as 4.3.12.3 and 4.3.15.3. 

L2 is now in the TS section

L2 is now in the TS section of the R&S lab: https://learningnetwork.cisco.com/docs/DOC-10859 ...L2 is in the TS workbook from day one because the TS workbook was written not just to prepare the students for the TS section of the lab, but also to summarize, test and sharpen the skills of the CCIE R&S students. Please notice that although the TS section is the first section of the lab, I recommend to practice the TS section after doing technology focused labs and moc labs.

[IPv6] Subnetting – Wait, we still need to do that?

Subnetting, in short, can be thought of as an adjustable “slide rule” that tells the network infrastructure the logical size of a sub-network, or subnet. This is useful if you know how many IP addresses you’ll to suit the needs of a predetermined number of PCs, so you can plan the size of your subnets to match that requirement. With IPv4, subnet masks are used to determine how big the subnets are.

[IPv6] Subnetting – Wait, we still need to do that?

Subnetting, in short, can be thought of as an adjustable “slide rule” that tells the network infrastructure the logical size of a sub-network, or subnet. This is useful if you know how many IP addresses you’ll to suit the needs of a predetermined number of PCs, so you can plan the size of your subnets to match that requirement. With IPv4, subnet masks are used to determine how big the subnets are.

[IPv6] Subnetting – Wait, we still need to do that?

Subnetting, in short, can be thought of as an adjustable “slide rule” that tells the network infrastructure the logical size of a sub-network, or subnet. This is useful if you know how many IP addresses you’ll to suit the needs of a predetermined number of PCs, so you can plan the size of your subnets to match that requirement. With IPv4, subnet masks are used to determine how big the subnets are.

Troubleshooting OSPFv2 Neighbors (Part 1)

Tackling one of the simplest OSPFv2 adjacency problems to the trained eye. Yet, it’s really incredible how often it can escape even the most seasoned veteran. Getting right to the point,...

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New Cisco IOS releases in an RSS feed

Over the last few days we've been spending some time on an RSS feed generator which can help you stay on top of new IOS releases. It takes regular expressions as input and can be useful for a quick search or generating an RSS feed for your favorite news reader.

The database is built upon a public md5 database Cisco publishes roughly every week. I cannot vouch for the accuracy of this information.

You can find the quick search & rss generator at http://snijders-it.nl/ios-rss/.

LISP + GETVPN as alternative for DMPVN+OSPF+GETVPN

Originally LISP was developed to address the issues and concerns raised by the growth of the internet routing table, but LISP turns out to possess appealing features that can be of interest to Service Providers like my friends at InTouch.

At the Cisco NAG2010 conference in San Jose I talked about using LISP as a transport mechanism instead of regular manual GRE tunnels or a DMVPN design. I believe that provisioning and debugging a LISP based virtual private network will be easier and simpler than current approaches.

Some fair warnings are in order here: this setup runs on beta IOS and NXOS images, this design and the configuration syntax are very likely to change a little with every IOS release, for Cisco's LISP implementation is under very active development. The most important aspect of this design is that it's not a multi-tenant architecture. Multi-tenancy will probably be available in a few months, after which I'll post an updated version with more comments on the specifics.

View the slides online at slideshare: LISP+GETVPN or download the PDF from my website: Job_Snijders-InTouch-LISP_GETVPN.pdf.
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