In Cisco Switches for VTP, what frame tagging protocol they support?

Cisco switches support two frame tagging protocols: Inter-Switch Link (ISL) IEEE 802.1Q Inter-Switch Link (ISL) It is Cisco’s proprietary frame tagging protocol.  It encapsulates a frame with an additional header (26 bytes) and trailer (4bytes). It increases the size of a frame by 30 bytes. The header contains several fields, including a 15-bit VLAN ID. [...]



If there are multiple EIGRP and OSPF neighborship flap over the GRE tunnel what could be the problem and how would solve it?

If in the logging you are getting the error message %TUN-5-RECURDOWN: Tunnel0 temporarily disabled due to recursive routing It means that GRE Router tunnel has found a recursive routing problem. The symptoms of this issue include the continous flapping of tunnel interface as well as EIGRP,OSPF & BGP neighbours when neighbours are over the GRE. [...]

How to configure GLBP?

Gateway Load Balancing Protocol (GLBP) provides redundancy for IP networks, ensuring that user traffic immediately and transparently recovers from first hop router failures, while allowing packet load sharing between a group of redundant routers. GLBP provides load balancing over multiple routers (gateways) using a single virtual IP address and multiple virtual MAC addresses. Each host is [...]

What is VSS?

The Virtual Switching System (VSS) is a clustering technology that combines two Cisco Catalyst 4500 or 6500 Series into a single virtual switch. In a VSS, the data plane of both clustered switches is active at the same time in both chassis. VSS members are connected by virtual switch links (VSLs) using standard Gigabit or 10 Gigabit [...]

Useful BGP commands on Cisco Routers

When BGP is not behaving correctly, a “trick” to temporarily stop peering with a neighbor is to use the following command: router bgp 194 neighbor<ipaddress> password xxx Since the other router doesn’t have the same password, the two routers will stop talking to one another, without you having to do anything else. Later, when the [...]

How to use the embedded wireshark in Cisco 3850 switches to capture the traffic

On the 3850 switches has embedded wireshark that can be used to packet capture during the troubleshooting this negate the need of SPAN to capture the traffic. -Define your source monitor capture mycap interface GigabitEthernet1/0/1 both -Set your match statement monitor capture mycap access-list myacl monitor capture mycap match ipv4 any any -Set your destination [...]

What is BFD?

Bidirectional Forwarding Detection (BFD) provides a low-overhead, short-duration method of detecting failures in the forwarding path between two adjacent routers, including the interfaces, data links, and forwarding planes. BFD is a detection protocol that you enable at the interface and routing protocol levels. Cisco supports the BFD asynchronous mode, which depends on the sending of [...]

Palo Alto CLI cheat sheet

Device management: Show general system-health information –> show system info Show percent usage of disk partitions –> show system disk-space Show the maximum log file size –> show system logdb-quota Show running processes –> show system software status Show processes running in the management plane –> show system resources Show resource utilization in the dataplane –> show running resource-monitor Show the [...]

What is VDC’s in Nexus Switches?

Cisco Nexus 7000 Series switches can be segmented into virtual devices based on customer requirements. VDCs offer several benefits e.g. fault isolation, administration plane, separation of data traffic, and enhanced security. This logical separation provides the following  benefits: Administrative and management separation Change and failure domain isolation from other VDCs Address, VLAN, VRF, and vPC isolation Each VDC acts as an [...]

OSI layer in short with example

7. Application layer-Responsible for initiating or services the request. e.g SMTP, DNS, HTTP, and Telnet 6. Presentation layer-Formats the information so that it is understood by the receiving system e.g Compression and encryption depending on the implementation 5. Session layer– Responsible for establishing, managing, and terminating the session e.g NetBIOS 4. Transport layer-Breaks information into [...]

Important CLI commands for F5 LTM


Hardware terms



Vlan trunking -Vlan divides the broadcast domain -In New switch, Default Vlan = Native Vlan = Vlan 1 -Native Vlan can be changed from Vlan 1 to Vlan10, 20 etc. -Vlan 1 cannot be deleted even after entering command -Vlan 1 carries critical traffic like CDP, VTP etc. -Access port carries traffic of only one [...]

How DHCP works?

The Dynamic Host Configuration Protocol (DHCP) is a standardized network protocol used on Internet Protocol (IP) networks. The DHCP protocol is controlled by a DHCP server that dynamically distributes network configuration parameters, such as IP addresses, for interfaces and services. A router or a residential gateway can be enabled to act as a DHCP server. [...]

What is UDLD?

Unidirectional Link Detection (UDLD) is a data link (layer 2) protocol from Cisco Systems to monitor the physical configuration of the cables and detect unidirectional links. UDLD allow two switches to verify if they can both send and receive data on a point-to-point connection.UDLD works with the Layer 1 (L1) mechanisms to determine the physical [...]

What is metro ethernet?


How HTTP protocol works?


How to setup the internet access through the Cisco ASA firewall?

Basic Guidelines for setting Internet through the Cisco ASA firewall: At first we need to configure the interfaces on the firewall. !— Configure the outside interface. interface GigabitEthernet0/0 nameif outside security-level 0 ip address !— Configure the inside interface. interface GigabitEthernet0/1 nameif inside security-level 100 ip address The nameif command gives [...]

What are the NAT syntax changes in the Cisco ASA firewall

There are major nat syntax changes after the ASA firewall iOS version 8.3. Regular static NAT: In the pre 8.3- static (inside,outside) net mask In the version 8.3 and later- object network obj- host nat (inside,outside) static Regular static PAT: In the pre 8.3- static (inside,outside) tcp 80 [...]

What is ICMP?
