IP Fragmentation

Some basic info

Ethernet header is 14bytes

TCP header is 40byes

standard IP MTU is 1500bytes

DF is not set 

find MTU of source

powershell to see max MTU of win11:

netsh interface ipv4 show interfaces 

Send some test traffic that is bigger than the MTU of the source

ping -l 1600 <destination>

Check with wireshark at destination

fragmented in 2 packets

first packet

second packet

DF is set

Send some test traffic that is bigger than the MTU of the source 

ping -l 1600 -f <destination>

packet will be dropped at the laptop

Wireshark display GRE packets

 

display filter ip.proto == 47

Add colummn with the following details:

VRF Route leaking via static routes

R1

10.170.138.14

|

|

Gi1/9-10.170.138.13

SW001(VRF INTERNET)

|

SW001(GLOBAL)

|

SW001(VRF ATT)

Gi1/2-10.170.137.2

|

|

Gi1/1-10.170.137.1

Router

|

|

network

|

|

10.0.29.3

To achieve this, we do vrf route leaking via static routes. It is not possible to leak directly between to vrfs, but it is possible between vrf and global in both directions.

On SW001:
VRF INTERNET (leak destination to global)
ip route vrf INTERNET 10.0.29.3 255.255.255.255 10.170.137.1 global

VRF ATT (leak source to global)
ip route vrf ATT 10.170.138.14 255.255.255.255 10.170.138.14 global

GLOBAL (static route to next-hops defined in static routes above)
ip route 10.170.137.1 255.255.255.255 GigabitEthernet1/2
ip route 10.170.138.14 255.255.255.255 GigabitEthernet1/9

NAT and PAT on ASA

 Best reference

https://www.practicalnetworking.net/stand-alone/cisco-asa-nat/

mac securecrt send cisco break to rommon

 in securecrt configure session with VT220 keyboard mapping and press F5 continuously when the router boots.

OpenWRT linksys with TC and NETEM

 

install openwrt on e4200v2 

Open ssh and http on the WAN (disable firewall)

Via GUI of openwrt (LuCi) install tc-full and kmod-netem

Inject some delay:

tc qdisc add dev internet root netem delay 10ms

Disable delay:

tc qdisc del dev internet root

tc -s qdisc ls dev internet

vmware esxi letsencrypt certificate

 Good info on how to install ssl certificate on esxi

(note that I run 6.5 which only seems to work with w2c 1.0.0)

https://github.com/w2c/letsencrypt-esxi/wiki/Installation-via-Web-UI

https://www.it-connect.fr/vmware-esxi-lets-encrypt-la-solution-pour-obtenir-un-certificat-ssl-gratuit/