CDP (Cisco Discovery Protocol) / LLDP (Link Layer Discovery Protocol) – protocols, allowing network devices to announce they presence to other devices. CDP – Cisco proprietary protocol, therefore it is working only with Cisco devices. LLDP – open protocol. Usage examples Best practice / configuration examples CDP enabled by default on all cisco devices. Best […]
HSRP (Hot Standby Routing Protocol) – Cisco proprietary protocol used for first hop redundancy. FHRP (First Hop Redundancy Protocol) – open protocol for same goal: first hop redundancy. 2 switches required for implementation. HSRP using virtual MAC and virtual IP to process packets. (And yes, in our case it is working on VLAN interfaces). Sample […]
VRF – Virtual Routing and Forwarding. Basically it is virtual router within physical router. With separated configuration and routing tables/databases. To use VRF, interface(or subinterface) should be assigned to VRF. Sample configuration. Basic VRF configuration: Add interface to VRF: Static route for VRF: Configure Dynamic routing for VRF (OSPF as example):
SVI – Switched Virtual Interface. Virtual interface on Cisco device, that connects and route traffic between devices in a VLAN. It allows switch to communicate with other devices in VLAN, such as computers or servers and allow routing between them and external networks (with some extra configuration of switch). Sample configuration:
Two most useful modes at which ports on switch can work is ‘access’ and ‘trunk’ mode. Access mode – all incoming traffic tagged with VLAN tag by switch and processed further. Outgoing traffic for this port processed only for associated VLAN. Trunk mode – allows VLAN/tagged incoming traffic and sort out incoming traffic basing on […]
Oxidized is a network device configuration backup tool. Wery useful, when you have hundreeds of switches/routers and want to keep configuration of mentioned devices and configuration version history. Open ports 80/tcp and 443/tcp: #firewall-cmd –add-port=80/tcp #firewall-cmd –add-port=443/tcp #firewall-cmd –runtime-to-permanent #firewall-cmd –reload Create directory for service: #mkdir /opt/oxidized Create shell script for Oxidized and make it […]
Check current configuration. Maybe rule already present? #iptables -t nat -L -n Save current configuration to file. #iptables-save > /etc/sysconfig/some_file_you_want Edit configuration file. #vi /etc/sysconfig/some_file_you_want For Destination NAT add record to PREROUTING section. Sample: All incoming traffic to IP 10.10.10.10 and port tcp/443 NAT-ed to IP 192.168.0.10 port tcp/10000 -A PREROUTING -d 65.87.230.18/32 -p tcp […]
Swap is used for cases, when system run out of available RAM. If server have no available RAM for process, it will crush/hung. Swap way extremely low, comparable to RAM and add extra load to disks. When you run a lot of Linux servers it is a great idea to have “swap cleaner” clear up […]
MTU in networks is Maximum Transmission Unit. And basically, it indicates the maximum size of packet what could be processed by network device without fragmentation. The default MTU is 1500, therefore, all packets what is bigger than 1500 bytes, should be fragmented to successfully transferred by network devices. Misconfiguration of MTU on different sides of […]
First i should mention: Playing mindlessly with this could lead to server instability. In some cases, some applications “eats” unbelievable amount of memory for buffers/cache, what could lead to different negative outcomes.For example, if server has 48Gb of RAM and some application uses 40Gb of this RAM for buffer/cache, it might be a good idea […]