Category: Networking

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

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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MACSec – Media Access Control Security

Media Access Control Security or MACSec is the Layer 2 hop to hop network traffic protection.

Just like IPsec protects network layer, and SSL protects application data, MACSec protects traffic at data link layer (Layer 2).

MACSec is standardized IEEE 802.1AE hop-by-hop encryption that enables confidentiality and integrity of data at layer 2.

It encrypts entire Ethernet packet except Source and Destination MAC addresses on any device-to-device, switch-to-switch, router-to-switch, host-to-switch directly connected wired L2 connection.


If we compare MACSec with, for example, IPsec, MACsec provides same security but on layer 2 for each hop separately. On each hop, packets are received and decrypted enabling other features like QoS and load balancing to function. Same data is again encrypted before being sent out to next device on the way towards the destination. MACsec works on host-to-switch connection and on switch-to-switch connection enabling line-rate up to 10 GigabitEthernet fast encryption.

It uses, especially for that occasion developed and optimised Galois/Counter Mode Advanced Encryption Standard 128 (GCM-AES-128) which makes line-rate encryption/decryption possible.

There is some difference in MACSec on the connection between host and switch, and MACSec on the connection from switch to switch

MACsec uses MACsec Key Agreement (MKA) which is standardized protocol to provide the required session keys and manages the required encryption keys on a MACSec connection between hosts (PC, server, etc.) and switch.

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Reflexive Access List

Some of my readers commented on my old article about reflexive access-list with issues in the configuration. I tried it in the lab again to be sure I didn’t make any mistake in the configuration example and here I’m sharing the lab and the config used.

About Reflexive Access Lists

Extended ACLs are a special kind of extended access-lists that have limited stateful behaviour technique implemented for TCP sessions. It is better to say that reflexive access-list is simulating stateful behaviour because it, by use of ‘established’ command, is allowing TCP packets that have the ‘ACK’ bit set but not the initial ‘SYN-only’ packet. In this way, we are effectively permitting only the packets that are part of an established session.

In my prior article, I showed how this works by enabling PING from PC1 in VLAN 10 to PC2 in VLAN 20 but not the other way.

I created the lab topology in GNS3:

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