IP address and Subnetting

IP ADDRESS & SUBNETTING Private IP addressing – Subnet Mask calculation – If the CIDR value is /25 then subnet mask will be – 255.255.255.128. In binary – 11111111.11111111.11111111.10000000  (8+8+8+1 = 25) Same way if subnet mask is – 255.255.192.0 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 [...]

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 [...]

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 [...]

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

TMOS commands run util bash -enable shell show sys self-ip -show self IP’s show ltm persistence persist-records -show persistence records list ltm node [node_address] -show node status modify ltm node [node_address] down -disable node modify ltm node [node_address] up -enable node modify net packet-filter all logging enabled -enable logging for all packet filters delete ltm [...]

Hardware terms

Bandwidth Bandwidth refers to the amount of information that can be transmitted over a network in a given amount of time, usually expressed in bits per second or bps Protocol Protocols are the set of rules / algorithm used to learn routes, so that network traffic can be passed from a source to the destination. [...]

VLAN, TRUNKING, VTP

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?

A metropolitan-area Ethernet, Ethernet MAN, or metro Ethernet network is a metropolitan area network (MAN) that is based on Ethernet standards. It is commonly used to connect subscribers to a larger service network or the Internet. Businesses can also use metropolitan-area Ethernet to connect their own offices to each other. An Ethernet interface is much [...]

How HTTP protocol works?

HTTP functions as a request–response protocol in the client–server computing model. A web browser, for example, may be the client and an application running on a computer hosting a web site may be the server. The client submits an HTTP request message to the server. The server, which provides resources such as HTML files and [...]

What is ICMP?

ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both control and error messages.

Acronyms

A • AAL: ATM Adaptation Layer • ABM: Asynchronous Balance Mode • ABR: Available Bit Rate • AC: Access Control • ACK: Acknowledgment • ADSL: Asymmetric Digital Subscriber Links • ANI: Automatic Number Identification • ANSI: American National Standards Institute • API: Application Programming Interface • ARM: Asynchronous Response Mode • ARP: Address Resolution Protocol [...]

Cisco ASA troubleshooting commands

AAA debug radius debug tacacs show aaa-server protocol PROTOCOL_NAME test aaa-server Access Control Lists show access-list show run | include ACCESS_LIST_NAME show run object-group show run time-range Application Inspection show conn state STATE_TYPE detail show service-policy Configuring Interfaces show firewall show int show int ip brief show ip show mode show nameif show run interface [...]

What is the use of default route?

In computer networking, the default route is a setting on a computer that defines the packet forwarding rule to use when no specific route can be determined for a given Internet Protocol (IP) destination address. All packets for destinations not established in the routing table are sent via the default route. The default route generally [...]

SNMP

Simple Network Management Protocol (SNMP) is an application–layer protocol defined by the Internet Architecture Board (IAB) in RFC1157 for exchanging management information between network devices. It is a part of Transmission Control Protocol⁄Internet Protocol (TCP⁄IP) protocol suite. SNMP is one of the widely accepted protocols to manage and monitor network elements. Most of the professional–grade [...]

How ARP works?

ARP stands for Address Resolution Protocol. When you try to ping an IP address on your local network, say 192.168.1.1, your system has to turn the IP address 192.168.1.1 into a MAC address. This involves using ARP to resolve the address, hence its name. Systems keep an ARP look-up table where they store information about [...]

How Load balancer works?

A load balancer is a device that acts as a reverse proxy and distributes network or application traffic across a number of servers. Load balancers are used to increase capacity (concurrent users) and reliability of applications. They improve the overall performance of applications by decreasing the burden on servers associated with managing and maintaining application and [...]

TCP- Three way handshake

The Three-way handshake begins with the initiator sending a TCP segment with the SYN control bit flag set. TCP allows one side to establish a connection. The other side may either accept the connection or refuse it. If we consider this from application layer point of view, the side that is establishing the connection is [...]

SPAN

The SPAN feature, which is sometimes called port mirroring or port monitoring, selects network traffic for analysis by a network analyzer. The network analyzer can be a Cisco SwitchProbe device or other Remote Monitoring (RMON) probe.  

Cisco ASA firewall common troubleshooting commands part 1

Check the system status myfirewall/pri/act# show firewall Firewall mode: Router myfirewall/pri/act# show version Cisco Adaptive Security Appliance Software Version 9.1(1) Device Manager Version 7.1(1)52 Compiled on Wed 28-Nov-12 10:38 by builders System image file is “disk0:/asa911-k8.bin” Config file at boot was “startup-config” myfirewall up 218 days 1 hour failover cluster up 5 years 10 days [...]

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 [...]