Category: Networking

The New Way of Generating IPv6 – SLAAC EUI-64 Address Format

There was an old way of generating Interface IPv6 address using SLAAC process (Stateless autoconfiguration). You simply configured that you want SLAAC autoconfiguration and the interface IPv6 was generated by squeezing “FFFE” in hex (11111111 11111110 bits) between two parts of physical MAC address of that interface.

Then, after a while, several comments came to IETF about the use of predictable Interface Identifiers in IPv6 addresses. They were pointing to the ease of correlation of host activities within the same network and across multiple networks. If Interface Identifiers are constant across networks this is negatively affecting the privacy and security of users on that network.

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Create or Edit a File on Cisco IOS Flash

There is always the option to edit a file locally on your computer in notepad++ and then upload it to Cisco device.

With this trick, you can write or edit a file from Flash memory directly from Cisco IOS console. If you need it for whatever reason, maybe to change something in the config file or something else, this is the way to do it.

I was using if for my next article lab where I needed a file on the flash with at least 1600 bytes so I can pull it from neighbouring router with HTTP and check some details in new TCP connection. It was faster to just create the file directly on the router flash and not creating it on my laptop and then transferring it with FTP or TFTP.

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Link Aggregation – LACP Protocol

EtherChannel enables bundling multiple physical links connecting same devices into a single logical link. I will try to show you how it is configured and how it works.

The issue with one uplink

I made an example with 8 clients connected to two Cisco 3850 switches. For start, those two switches are connected together with 1G copper on Interface Ge1/23. The clients are also connected to 1G ports. In this case, when all of those four clients on the left side start simultaneously sending traffic at full speed to different computers on the right side, they will congest the uplink between switches and some traffic will be dropped.

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Check Point Firewall VM Disk Resize

It is related to Check Point MGMT VM with R80.10 in my story, but you would as well want to resize Check Point gateway firewall hardware box or VM.

I was searching for a simple solution and found different ones that didn’t work for me, so here are the steps that you need to go through when you resize your CheckPoint VM disk in vCenter and then need to expand the partition inside Check Point VM in order to use the additional space.

Of course, you did choose too small HDD for your VM when you created it and now you cannot upload some hotfixes or vSEC gateway files to it because you don’t have enough space.

Get to vCenter and shut down the VM.

vCenter VM Shutdown

Get more GB to your VM and power it back up.

vCenter VM HDD Space Increase

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IPv6 Generated with EUI-64 Has a Strange Bit Inside

UPDATE on 22 Mar 2018:
Although the article is correctly explaining the IPv6 address generated in the example at the bottom, it seems that the process of generating the IPv6 address with EUI-64 has been changed from what is described in RFC2373 to something like RFC4291 and then to something like RFC7217. Thanks to @FernandoGont for pointing to this issue. A new article is here which describes newly suggested technique on how SLAAC implementation should work in new network device/NIC implementations.

What is universal/local bit in IPv6 EUI-64 address?

One of my readers contacted me with an interesting question in comments of “IPv6 – SLAAC EUI-64 Address Format” article. The question was:

“How come that the ipv6 address after the prefix is 21C:C4FF:FECF:4ED0 if the mac address is 00-1C-C4-CF-4E-D0?”

Of course, we all know from the previous article that EUI-64 process is taking the interface MAC address (if that is an Ethernet interface) and it creates 64 bits Interface ID with it by shimming additional FFFE (16bits in hex) in between the MAC address bits.

The reader was confused with an additional change that I did not cover in that article which is called universal/local bit of the IPv6 address Interface ID part.

Let’s go.

IPv6 address is 128 bit. First ‘n’ bits (first 64 bits of EUI-64 created IPv6 address) are called “subnet prefix” and the other half of bits are called “Interface ID”.

If we use EUI-64 process to generate a unique IPv6 address of the interface, then we are generating Interface ID from MAC address (or some other kind of L2 address if this is not about Ethernet).

|                     n bits                     |   128-n bits   |
+------------------------------------------------+----------------+
|                  subnet prefix                 |  interface ID  |
+------------------------------------------------+----------------+

On RFC 2373 page 18 chapter: “APPENDIX A : Creating EUI-64 based Interface Identifiers”, you can find that 7th bit on Interface ID part of an IPv6 address (the last 64 bits) is called “universal/local bit”.

If this bit is set to “0” it indicates local scope IPv6 address and if it is “1” then the generated IPv6 address has global scope (it is globally unique).

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