F5 LTM Troubleshooting- Things to check if Pool member is down

Check if the server is reachable from the F5 Load balancer [root@bigip118:Active:Standalone] config # ping PING ( 56(84) bytes of data. 64 bytes from icmp_seq=1 ttl=255 time=3.83 ms 64 bytes from icmp_seq=2 ttl=255 time=2.88 ms ———————————————————— If you want to ping from particular vlan you can specify vlan name after –I [...]

IP address and Subnetting

IP ADDRESS & SUBNETTING Private IP addressing – Subnet Mask calculation – If the CIDR value is /25 then subnet mask will be – In binary – 11111111.11111111.11111111.10000000  (8+8+8+1 = 25) Same way if subnet mask is – the CIDR value will be /18 (8+8+2) Wild card calculation – Whatever the subnet mask [...]

What are the STP times?

 Hello Timer  Forward delay Timer  Max-age Timer   Hello Timer: How often switches send BPDU’s by default every 2 seconds Forward delay Timer: how much long a port must spend time in both learning and listening state. By default 15 seconds Max-age Timer: How long a switch will retain BPDU information from a neighbor switch [...]

Why we use Spanning Tree Protocol in the Switches?

 Broadcast Storms Duplicate Frame copies Unstable MAC Table   Broadcast Storms Without any loop removing mechanism, switches will flood broadcasts endlessly throughout the network. This is known as broadcast storm. Duplicate Frame copies A device could receive duplicate copies of same frame from different switches. It creates additional overhead on the network. Unstable MAC Table [...]

What are the link aggregation protocols in Cisco Switches, what are their modes required to bundle a link?

Dynamic Configuration Cisco switches support two dynamic aggregation protocols: PAgP (Port Aggregation Protocol) – Cisco proprietary aggregating protocol. LACP (Link Aggregation Control Protocol) – IEEE standardized aggregation protocol, originally defined in 802.3ad. PAgP and LACP are not compatible – both sides of an Etherchannel must use the same aggregation protocol. EthernChannel – PAgP It supports [...]

A receiving host computes the checksum on a frame and determines that the frame is damaged. The frame is then discarded. At which OSI layer did this happen?

The Data Link layer provides the physical transmission of the data and handles error notification, network topology, and flow control. The Data Link layer formats the message into pieces, each called a data frame, and adds a customized header containing the hardware destination and source address. Protocols Data Unit (PDU) on Datalink layer is called [...]

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 [...]