Ping Error Messages - Networking Computer Tips

To block from ping respond

#iptables –A INPUT –P icmp –icmp-type echo-request –j DROP

Linux Iptables allow or block ICMP ping request

The Internet Control Message Protocol (ICMP) has many messages that are identified

by a "type" field. You need to use 0 and 8 ICMP code types.

=> Zero (0) is for echo-reply

=> Eight (8) is for echo-request.

To enable ICMP ping incoming client request use following iptables rule (you need to

add following rules to script).

My default firewall policy is blocking everything.

Task: Enable or allow ICMP ping incoming client request

Rule to enable ICMP ping incoming client request ( assuming that default iptables policy

is to drop all INPUT and OUTPUT packets)

SERVER_IP="202.54.10.20"

iptables -A INPUT -p icmp --icmp-type 8 -s 0/0 -d $SERVER_IP -m

state --state NEW,ESTABLISHED,RELATED -j ACCEPT

iptables -A OUTPUT -p icmp --icmp-type 0 -s $SERVER_IP -d 0/0 -m

state --state ESTABLISHED,RELATED -j ACCEPT

Task: Allow or enable outgoing ping request

To enable ICMP ping outgoing request use following iptables rule:

SERVER_IP="202.54.10.20"

iptables -A OUTPUT -p icmp --icmp-type 8 -s $SERVER_IP -d 0/0 -m

state --state NEW,ESTABLISHED,RELATED -j ACCEPT

iptables -A INPUT -p icmp --icmp-type 0 -s 0/0 -d $SERVER_IP -m

state --state ESTABLISHED,RELATED -j ACCEPT

How do I disable outgoing ICMP request?

Use the following rules:

iptables -A OUTPUT -p icmp --icmp-type echo-request -j DROP

OR

iptables -A OUTPUT -p icmp --icmp-type 8 -j DROP

ICMP echo-request type will be block by above rule.

See ICMP TYPE NUMBERS (type fields). You can also get list of ICMP types, just type

following command at shell prompt:

# /sbin/iptables -p icmp -h

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PING (Packet Internet Groper) is a program used to test whether a particular network host is online by sending an ICMP (Internet control message protocol) echo request and waiting for a response. It is used for troubleshooting connectivity between network devices such as servers, routers, workstations and printers

TTL Expired in TransitThe TTL value determines the maximum amount of time an IP packet may live in the network without reaching its destination. It is effectively a bound on the number of routers an IP packet may pass through before being discarded. This message indicates that the TTL expired in transit. Number of required hops exceeds TTL. Increase TTL by using the ping -i switch.

Destination Host UnreachableThe host that you are trying to ping is down or is not operating on the network. A local or remote route does not exist for destination host. Modify the local route table or notify the router administrator.

Request Timed OutThe ping command timed out because there was no reply from the host. No Echo Reply messages were received due to network traffic, failure of the ARP request packet filtering, or router error. Increase the wait time using the ping -w switch.

Unknown HostThe IP Address or the Host Name does not exist in the network or the destination host name cannot be resolved. Verify name and availability of DNS servers.

TTL Expired in Transit

The number of hops required to reach the destination exceeds the TTL set by the sending host to forward the packets. The default TTL value for ICMP Echo Requests sent by Ping is 32. In some cases, this is not enough to travel the required number of links to a destination. You can increase the TTL using the -i switch, up to a maximum of 255 links.

If increasing the TTL value fails to resolve the problem, the packets are being forwarded in a routing loop, a circular path among routers. Use Tracert to track down the source of the routing loop, which appears as a repeated series of the same IP addresses in the Tracert report. Next, make an appropriate change to the routing tables, or inform the administrator of a remote router of the problem.

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Destination Host Unreachable

This message indicates one of two problems: either the local system has no route to the desired destination, or a remote router reports that it has no route to the destination. The two problems can be distinguished by the form of the message. If the message is simply "Destination Host Unreachable," then there is no route from the local system, and the packets to be sent were never put on the wire. Use the Route utility to check the local routing table.

If the message is "Reply From < IP address >: Destination Host Unreachable," then the routing problem occurred at a remote router, whose address is indicated by the "< IP address >" field. Use the appropriate utility or facility to check the IP routing table of the router assigned the IP address of < IP address >.

If you pinged using an IP address, retry it with a host name to ensure that the IP address you tried is correct.

Request Timed Out

This message indicates that no Echo Reply messages were received within the default time of 1 second. This can be due to many different causes; the most common include network congestion, failure of the ARP request, packet filtering, routing error, or a silent discard. Most often, it means that a route back to the sending host has failed. This might be because the

destination host does not know the route back to the sending host, or one of the intermediary routers does not know the route back, or even that the destination host's default gateway does not know the route back. Check the routing table of the destination host to see whether it has a route to the sending host before checking tables at the routers.

If the remote routing tables are correct and contain a valid route back to the sending host, to see if the ARP cache lacks the proper address, use the arp -acommand to print the contents of the ARP cache. Also, check the subnet mask to be sure that a remote address has not been interpreted as local.

Next, use Tracert to follow the route to the destination. While Tracert does not record the address of the last hop or the path that the packet followed on the return path, it might show that the packet made it to the destination. If this is the case, the problem is probably a routing issue on the return path. If the trace doesn't quite reach the destination, it might be because the target host is protected by a firewall. When a firewall protects the destination, ICMP packet filtering prevents the ping packets—or any other ICMP messages—from crossing the firewall and reaching their destination.

To check for network congestion, simply increase the allowed latency by setting a higher wait time with the -w switch, such as 5000 milliseconds. Try to ping the destination again. If the request still times out, congestion is not the problem; an address resolution problem or routing error is a more likely issue.

Unknown Host

This error message indicates that the requested host name cannot be resolved to its IP address; check that the name is entered correctly and that the DNS servers can resolve it.

Code Description

0 Network unreachable error.

1 Host unreachable error.

2 Protocol unreachable error (the designated transport protocol is not supported).

3Port unreachable error (the designated protocol is unable to inform the host of the incoming message).

4The datagram is too big. Packet fragmentation is required but the 'don't fragment' (DF) flag is on.

5 Source route failed error.

6 Destination network unknown error.

7 Destination host unknown error.

8 Source host isolated error (military use only).

9 The destination network is administratively prohibited.

10 The destination host is administratively prohibited.

11 The network is unreachable for Type Of Service.

12 The host is unreachable for Type Of Service.

13Communication administratively prohibited (administrative filtering prevents packet from being forwarded).

14Host precedence violation (indicates the requested precedence is not permitted for the combination of host or network and port).

15Precedence cutoff in effect (precedence of datagram is below the level set by the network administrators).

 The default TTL value for ICMP Echo Requests sent by Ping is 32.

OS/Device Version Protocol TTL

AIX TCP 60

AIX UDP 30

AIX 3.2, 4.1 ICMP 255

BSDI BSD/OS 3.1 and 4.0 ICMP 255

Compa Tru64 v5.0 ICMP 64

Cisco ICMP 254

DEC Pathworks V5 TCP and UDP 30

Foundry ICMP 64

FreeBSD 2.1R TCP and UDP 64

FreeBSD 3.4, 4.0 ICMP 255

FreeBSD 5 ICMP 64

HP-UX 9.0x TCP and UDP 30

HP-UX 10.01 TCP and UDP 64

HP-UX 10.2 ICMP 255

HP-UX 11 ICMP 255

HP-UX 11 TCP 64

Irix 5.3 TCP and UDP 60

Irix 6.x TCP and UDP 60

Irix 6.5.3, 6.5.8 ICMP 255

juniper ICMP 64

MPE/IX (HP) ICMP 200

Linux 2.0.x kernel ICMP 64

Linux 2.2.14 kernel ICMP 255

Linux 2.4 kernel ICMP 255

Linux Red Hat 9 ICMP and TCP 64

MacOS/MacTCP 2.0.x TCP and UDP 60

MacOS/MacTCP X (10.5.6) ICMP/TCP/UDP64

NetBSD ICMP 255

Netgear FVG318 ICMP and UDP 64

OpenBSD 2.6 & 2.7 ICMP 255

OpenVMS 07.01.2002 ICMP 255

OS/2 TCP/IP 3.0 64

OSF/1 V3.2A TCP 60

OSF/1 V3.2A UDP 30

Solaris 2.5.1, 2.6, 2.7, 2.8 ICMP 255

Solaris 2.8 TCP 64

Stratus TCP_OS ICMP 255

Stratus TCP_OS (14.2-) TCP and UDP 30

Stratus TCP_OS (14.3+) TCP and UDP 64

Stratus STCP ICMP/TCP/UDP60

SunOS 4.1.3/4.1.4 TCP and UDP 60

SunOS 5.7 ICMP and TCP 255

Ultrix V4.1/V4.2A TCP 60

Ultrix V4.1/V4.2A UDP 30

Ultrix V4.2 – 4.5 ICMP 255

VMS/Multinet TCP and UDP 64

VMS/TCPware TCP 60

VMS/TCPware UDP 64

VMS/Wollongong 1.1.1.1 TCP 128

VMS/Wollongong 1.1.1.1 UDP 30

VMS/UCX TCP and UDP 128

Windows for Workgroups TCP and UDP 32

Windows 95 TCP and UDP 32

Windows 98 ICMP 32

Windows 98, 98 SE ICMP 128

Windows 98 TCP 128

Windows NT 3.51 TCP and UDP 32

Windows NT 4.0 TCP and UDP 128

Windows NT 4.0 SP5- 32

Windows NT 4.0 SP6+ 128

WindowsNT 4 WRKS SP 3, SP 6a

ICMP 128

Windows NT 4 Server SP4 ICMP 128

Windows ME ICMP 128

Windows 2000 pro ICMP/TCP/UDP128

Windows 2000 family ICMP 128

Windows Server 2003 128

Windows XP ICMP/TCP/UDP128

.

7. Application Layer

NNTP  · SIP  · SSI  · DNS  · FTP  ·Gopher  · HT

TP  · NFS  · NTP  · SMPP  ·SMTP  · SNMP  · Te

lnet  · DHCP  ·Netconf  · RTP  · SPDY  · (more)

6. Presentation Layer

MIME  · XDR  · TLS  · SSL

5. Session Layer

Named Pipes  · NetBIOS  · SAP  · L2TP · PPTP · SOCKS

4. Transport Layer

TCP  · UDP  · SCTP  · DCCP  · SPX

3. Network Layer

IP (IPv4, IPv6) · ICMP  · IPsec  · IGMP  ·IPX  · AppleTalk

2. Data Link Layer

ATM  · SDLC  · HDLC  · ARP  · CSLIP  ·SLIP  · GFP  · PLIP  · IEEE   802.3   ·Frame   Relay   · ITU

-T   G.hn   DLL   · PPP  ·X.25  · Network Switch  ·

1. Physical Layer

EIA/TIA-232  · EIA/TIA-449  · ITU-T   V-Series   · I.430  · I.431  · POTS  · PDH  ·SONET/SDH  · PON  · OTN  · DSL  ·IEEE   802.3   · IEEE   802.11  

·IEEE   802.15   · IEEE   802.16   · IEEE   1394 · ITU

-T   G.hn   PHY   · USB  · Bluetooth  ·Hubs

o Access… Run Command

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Windows Magnifier magnify

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Windows Picture Import Wizard (need camera connected) wiaacmgr

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Windows Update Launches wupdmgr

Windows Version (to show which version of windows) winver

Windows XP Tour Wizard tourstart

Wordpad write

diff b/w hub,switch,bridge,router

http://www.nutt.net/2004/11/20/difference-in-hub-switch-bridge-router/

Difference in Hub, Switch, Bridge, & Router | Nutt.net

www.nutt.net

In an ethernet network there are 4 devices that from the the outside look very similar. In this article we will look at the difference between hubs, switches, bridges, and routers.

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Like ·  · Follow Post · Share · 7 hours ago near Chennai

Muthu Kumaran Loganathan Hub: 1) Unintelligent Device 2) No Technology to handle MAC information 3) No memory 4) It gets the data from one port, regenerates the data and sends the data to all ports. 5) Also called as multi port Repeater.

2 hours ago · Like

Muthu Kumaran Loganathan Switch: 1) Intelligent Device 2) It has RAM to handle MAC information 3) It forwards the data with the help of MAT(MAC Address Table) 4) It has a specialized hardware called ASICS (Application Specific Integrated Circuits)

2 hours ago · Like

Muthu Kumaran Loganathan Router: 1) Used to communicate between different Networks. 2) It provides WAN Connectivity 3) It can read IP Header information. 4) It maintains IP routing table which contains best paths to reach destination networks.

2 hours ago · Like

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 /windows/system32/drivers/etc/hosts file...

2 hours ago · Like

The proxy is not applied in the above scenario.. that's the question... So we need to check in the Hosts file... EX: If you give 127.0.0.1 yahoo.com, it will assign that yahoo.com ip is 127.0.0.1, but it is a loop back ip.. so You can't able

II.ROUTING PROTOCOLS

Most of the routing algorithms they are possible to be classified like one of two basic algorithms:

Distance Vector and Link-State.

1. Distance Vector characteristics: 3

(1 collects data of the information of the routing table of its neighbors.

(2) determines the best route adding the metric value that receives

as the routing information happens from router to another one.

(3) With most of the protocols of routing by distance vector, the updates for the changes of

topology consist of periodic updates of the tables.

RIP and EIGRP are examples of vector distance protocols.

2. Link state characteristics:

(1) The link state routing obtains a great vision of the topology of complete internetwork

accumulating all the necessary LSA.

(2) In the link state routing, each router it works independently to calculate its own shorter route

towards the networks destiny.

(3) With the protocols of routing of connection state, the updates are caused generally by

changes in the topology. The relatively small LSA that have gone to all the others routers

generally give like result faster times of convergence with any change of topology of the

internetwork.

OSPF it’s an example of link state protocol.

A. Routing information protocol (RIP)

d. RIP characteristics:

(1) Distance vector routing protocol.

(2) It metric is the number of jumps.

(3) The maximum number of jumps is 15 4

(4) One updates every 30 seconds

(5) Not always it selects the fastest route for the packages

(6) It generates great amount of traffic of network with updates.

Another one of the problems that the use of the RIP presents is that sometimes a destiny can be

located too much far like being attainable. The RIP allows fifteen as maximum limit for the

number of jumps through which data can be sent. The network destiny is considered unreachable

if there are more than fifteen jumps of router.

B. Enhanced Interior Gateway Routing Protocol (EIGRP)

As its name suggests, EIGRP is an enhanced version of IGRP (Interior Gateway Routing

Protocol), an obsolete routing protocol that was developed by Cisco

EIGRP sends partial updates

when a metric or the topology on the network changes. It does not send full routing-table updates

in periodic fashion as distance-vector protocols do. EIGRP is a classless protocol that permits the

use of VLSMs (Variable Length Subnet Masks) and supports CIDR (Classless Inter-Domain

Routing) for a scalable allocation of IP addresses.

EIGRP uses the metrics like bandwidth, delay, reliability, load, and MTU in making its routing

decisions .The default metrics used are bandwidth and delay. For a more granular level of control,

EIGRP multiplies each of the metrics by 256 before performing the calculation of the composite

metric. EIGRP has been designed to make much better use of bandwidth, and to allow routers to

have a much better awareness of neighboring routers. Instead of sending its entire routing table

out at regular intervals, an EIGRP router sends out only partial updates, and even then, only

when a route changes. This makes a better use of the available network bandwidth. An EIGRP

router also has a more complete view of the network than a typical distance vector protocol as it

not only maintains its own routing table, but also keeps a copy of the routing tables of

neighboring routers. When an EIGRP router cannot find a route to a network based on all the

information it currently has, it sends out a query to other routers, which is propagated until a

route is found.

C. Open shortest path first (OSPF)

(1) Fast detection of changes in the topology and very fast reestablishment of routes without

loops.

(2) Low overload, use updates that inform about changes on routes.

(3) Division of traffic by several equivalent routes.

(4) Routing according type of service.

(5) Use of multi-send in local area networks.

(6) Subnet and Super-net mask.

(7) Authentication

III. SIMULATION

1. Simulation Methodology

Network is simulated using OPNET® Modeler. OPNET®