Month: December 2014

FB DISCUSSIONS: CONGESTION ON LINK: CHECK, TROUBLESHOOT & SOLUTION


how can we check congestion on link and what all parameters and commands to check , if there is congestion on link . what all possible reason for congestion . what all possible steps for troubleshooting with commands

Like · ·
  •  
    Ikram Khan likes this.
  •  
    Fahad Ahmed As far as I know or remember their is a software called WAN optimizer ,you can try that.

    Or you can check on wireshark software.

  •  
    Sumit Sharma Fahad Ahmed .. WAN optimizer is a separate dedicate device. Its purpose is to utilize its mechanism, compression is part of mechanism in such a way that Bandwidth requirement is reduced. Most common is Steelhead Riverbed.
  •  
    Sumit Sharma In Steelhead Riverbed, There is one feature, We have the option of checking Top Talkers List, which tells us which ip or user or device is utilizing maximum bandwidth with exact amount of data.
  •  
    Sumit Sharma HOW TO CHECK CONGESTION ?
    ———————————–
    OPTION 1: Check Live traffic, using command show interface summary

    ———————————–
    OPTION 2: NFA is Netw Flow Analyezer.If NFA is configured, NFA also captures the traffic
    over different interfaces with more details
    ———————————–
    OPTION 3: If Riverbed is configured,
    we have feature called Top Talkers List to check exact amount of data for every ip
    ———————————–
    If the utilization is normal at a particular time,
    we need to observe the traffic trend at the peak time or office business hours
    •  
      Sumit Sharma If you know that there is congestion in the network,
      it means you already got the output that yes bandwidth utilization is high
      ——————————

      Normally, problem comes in like LATENCY in the network,
      for that one of the reason can be the congestion.
      ——————————
    •  
      Sumit Sharma SOLUTION
      ————–
      OPTION 1: Increase the Bandiwdth

      ————–
      OPTION 2: Deploy WAN optimizer device like Steelhead Riverbed
      ————–
      OPTION 3: Most of the time what happens is Two different servers are communicating with each other for backup. This traffic is utilization is maximum proportion of Bandwidth.
      Solution is to dedicate separate link for critical Datacenter servers communication or traffic
      ————-
      OPTION 4: Simply find the culprit user & try to decrease the utilization
      ————–
    •  
      Karan Puri what else if there is no wan optimizer in between ? Top talkers will help ?
    •  
      Sumit Sharma We can check list of Top Talkers, only on the Steelhead Riverbed device.

 

Advertisements

OSPF NEIGHBORSHIP FLAPPING


TROUBLESHOOTING STEPS

GIVEN SCENARIO

STEP 1: FAULTY SWITCH PORT

STEP 2: FAULTY  CABLE

STEP 3: FAULTY ROUTER PORT

STEP 4: SPEED / DUPLEX SETTINGS

STEP 5: OSPF HELLO / DEAD TIMER

STEP 6: CHECK CPU UTILIZATION


 

GIVEN SCENARIO

We have a Customer edge device or WAN device or Router at the Data center. The, comes the connected switch.

When we check the OSPF neighborship at  Router, neighborship with the connected switch is flapping continously.

This can be checked using command: show ip ospf nei | i Up

we need to troubleshoot the ospf neighborship flapping issue

 

PHYSICAL CONNECTIVITY

CUSTOMER EDGE DEVICE / WAN DEVICE / ROUTER (Gi0/1)  =============  SWITCH  


 

STEP 1: FAULTY SWITCH PORT

There might be the case that switch port is faulty. So, simply swap the switch port with any vacant port.

How to check vacant port ?

Port can be admin down, check using command: sh int des

If there is no admin down port, use command : sh int status, output will show “notconnected” ports

Suppose you ae able to find the notconnected port, as an example: Gi0/0

Check running configuration of Gi0/0. If the configuration is present, then check below steps to check further

Use command: sh ip arp Gi0/0, if interface is getting arp response or not, Port should not get arp response to use it further.

or,

Use command: sh int summary, to cross-check if there is any traffic on interface


 

STEP 2: FAULTY  CABLE

Cable connected between Router & Switch can be faulty.

Replace the cable between Router & Switch with a new one


 

STEP 3: FAULTY ROUTER PORT

Here, we suppose that the Router port is faulty.

OSPF is running on Router port. So, look for some other vacant port on Router.

Example: Current port is Gi0/1 & vacant port is Gi0/2.

First, remove the configuration from Gi0/1 & then paste the configuration on Gi0/2.

Take care of one more thing, new port Gi0/2 should be ” no shut ”

Symptoms

OSPF neighborship will go down during this process.

There will be no output in command: sh ip ospf nei

After changes,

You will see the output in below commands:

sh ip ospf int br

sh ip ospf nei

 

It means, things are fine as per changes performed

Now, check if OSPF is still flapping or not using command: sh ip ospf nei de | i Up


 

STEP 4: SPEED / DUPLEX SETTINGS

Confirm the speed / duplex settings on the Router & Switch port. Both should be matched


 

STEP 5: OSPF HELLO / DEAD TIMER

Check the OSPF Hello / Dead timers using command: sh ip ospf int, if the value is very low, not as per Cisco recommendations

As an example, if OSPF Hello timer is configured as 1/10th of a second, which is not recommended.

Then, there might be the case that due to high CPU utilization or busy CPU, Hello packets might get missed.

So, solution is to configure the Hello packet timers as 10 sec, as per Cisco recommendation


 

STEP 6: CHECK CPU UTILIZATION

Check the CPU utilization on Router & Switch both, if CPU utilization is high, Hello packets might get missed.


LAYER 2 vs LAYER 3 BROADCAST


hai everyone…
I’m confused with layer 2 broadcast and layer 3 broadcast…can u plz xplain with real scenario …thank in advance…

  •  
    You and 2 others like this.
  •  
    Yogesh Kokadwar Bhai mere layer 2 broadcast hota he Lekin layer 3 multicast hota he normally
    3 hrs · Like · 1
  •  
    Muhammad Khan 255.255.255.255 layer 3 b.cast
    ff:ff:ff:ff:ff layer 2 b.cast..
    In simple words
    2 hrs · Like · 3
  •  
    Binoj Sasidharan Layer 2 broadcasts are sent to the broadcast mac address ffff:ffff:ffff if ethernet and so can be received by any device in the same broadcast domain . Layer 3 broadcasts are sent to the broadcast network address, which for an ip network of 10.1.1.0/24 would be 10.1.1.255. If the IP network was over ethernet, a layer 3 broadcast would also result in a layer 2 broadcast
    • 2 hrs · Like · 1
    •  
      Abhi Singh Broadcast frames usually have a hosts MAC/IP address in the SA field.
      An example of a layer 2 broadcast is an ARP Request.
      in an ARP request Host A [IP=10.1.1.5 MAC=AA:B2.CD] knows the destination IP I want [10.1.1.11], but do not know the destination MAC address, so it is a unicast L3/broadcast L2.
      Frame [dMAC=ff:ff:ff][sMAC=AA:B2:CD][dIP=10.1.1.11][sIP=10.1.1.5][PDU]
      An example of a layer 3 broadcast is DHCP DISCOVER. My host knows its own MAC but doesn’t know my IP, I don’t know the destination IP or MAC so is broadcast L3 and broadcast L2
      Frame [dMAC=ff:ff:ff][sMAC=AA:B2:CD][dIP=255.255.255.255][sIP=0.0.0.0][PDU]
      2 hrs · Like · 4
    •  
      Abhi Singh Please advise Sumit Sharma Sir…
      1 hr · Unlike · 1
    •  
      Abhi Singh Need your input here…
      1 hr · Unlike · 1
    •  
      Sumit Sharma LAYER 2 BROADCAST
      ==> broadcast L2 frame has the dst MAC set to ff-ff-ff-ff-ff-ff.
      ==> Means broadcast will be done in a particular subnet only.
      So, Broadcast will stay inside the boundary of a single network or single subnet, where broadcast originated

 

 

OSPF DISCARD ROUTE


can anyone throw some light. Learning routes in routing table via ospf but it is showing as “discard” in the routing table.

What could be the possible reasons ?

Unlike · · · 57

 

 

WLC: UNDERSTANDING GUI: LIVE CONFIGURATION


TOTAL NUMBER OF PAGES IN WLC: NINE

wlc pages

PAGES COVERED IN POST

==> MONITOR

 

PAGE – MONITOR – SUMMARY

WLC MONITOR PAGE

 

PAGE – MONITOR – SUMMARY 

WLC HOMEPAGE

COMMENTS

==> Uptime shown is more than 207 days

==> Local Mobility Group shows the Mobility group name

==> This WLC can support maximum of 15 LAP’s, as per license installed

==> Port status of 1,2,3 & 4 is shown. Port 1 & 2 are up, whereas port 3 & 4 are down.

==> Software version is 7.0.230.0

==> CPU usage is also given

 

PAGE – MONITOR – SUMMARY 

WLC HOMEPAGE 2

COMMENTS:

==> In Access Point Summary, All APs = 5, which is showing the total number of associated AP’s. Click on details for further information.

==> In Access Point Summary, 802.11 a/n  &  802.11 b/g/n  are showing different bands.  In front of them, total number of AP’s are given supporting these bands

==> In Client summary, shows the user’s connected to WLC. Click on details for further information.

 

PAGE – MONITOR – SUMMARY 

HOMEPAGE ALL ACCESS DETAILS

COMMENTS

==> Details shown are list of all AP’s

==> Authentication used between AP & WLC is Internal Authorization. Internal Authorization means authentication using certificates, not using any external server. Here, certificate type is MIC. Other options are SSC, LSC.

==> Uptime for all the Ap’s are shown

==> AP mode is local. Other possible mode can be Flex connect mode.

 

PAGE – MONITOR – STATISTICS – AP JOIN

MONITOR AP JOIN

 

PAGE – MONITOR – STATISTICS – PORTS

MONITOR PORTS

 

 

PAGE – MONITOR – STATISTICS – RADIUS 

MONITOR RADIUS SERVERS

 

 

PAGE – MONITOR – CDP – INTERFACE NEIGHBORS

MONITOR CDP

 

COMMENTS

==> Here, Gi0/0/1  &  Gi0/0/2 are the ports on WLC.

==> In Neighbor name, connected devices host name is shown. Neighbor ip is the ip of connected devices to WLC.

==> Gi0/2  &  Gi0/3 are the ports of connected devices

 

PAGE – MONITOR – CDP – AP NEIGHBORS – CLICK DETAILS

MONITOR AP NEIGHBOR

 

COMMENTS

==> AP Name shows associated AP’s

==> Neighbor Name shows the name of connected devices, which should be a switch. Neighbor address is the ip address of the connected switch. Neighbor port is the connected port on switch.

 

 

VLAN, TRUNKING, VTP: OBJECTIVE QUESTIONS


 

 

 

 

 

 

 

 

 

 

 

 

FB DISCUSSIONS: HOW TO CHECK BANDWIDTH ?


Hi experts,

What would be the possible reason for not getting complete throughput on a link?

Scenario:- I have a 144 Mbps circuit but able to use 4 Mbps of it only.

Note-Port setting, policy setting and cabling has been already verified.

will appreciate your helps on it.

Thanks!!

  • You and 3 others like this.
  • Manjunath S Chickmath check the Quality of service (QOS) provided by Service provider or check on different port if that helps..
  • Sarvesh Dubey Hi Manjunath S Chickmath thanks for the reply, can you please share the way to check QOS on juniper router……..by the way the links belong to service provider itself for DCN , so As per my understanding QOS wouldn’t be an issue here
  • Munnawar Shaikh Can you post the configuration
  • Bharat Jaiswal is it abt wireless…?
  • Debu Chakrabarty Contact ISP for polished speed
    18 hrs · Like · 1
  • Sarvesh Dubey Hi Munnawar Shaikh I will post the configuration by today EOD, Bharat Jaiswal it is wire-line not wireless, Debu Chakrabarty this link is bening use for DCN to mange optical nodes of a service provider, policy on the router applied for this link is of 144Mbps only.
    12 hrs · Like · 1
  • Manish Yadav Refer data sheet of router and check router supports how much bandwidth capability overall.
    • 10 hrs · Like · 1
    • Sampath Kumar Dude remove the ISP cable from your switch put it directly to ur PC. configure static ip with the public provided by the ISP, now check the Bandwidth speed if u r getting 4MBPS only give a hard kick to isp provider. If you r getting the full bandwidth in your PC, then case1: any huge downloads may be going on, try to find in that way. case2: QOS policy is done on router or firewall to check that go through the running config of entire router(by using “|” (pipe symbl) may reduce ur burden). if qos is enabled remove it.
    • Manish Yadav for eg the router has capability of 160Mb . On router one 80 Mb link is terminated (i.e;occupied) and also other parameters consume bandwidth like hello,encryption,etc. remained with 40% of 160MB.
    • Manish Yadav Also check with ISP (end to end including third party vendor of ISP ) for B/W capping (rate-limit on router and MUX)
    • Abdul Wahid 1st check what is with isp is policy configured for 144. and informed to isp test link on ethernet tester, how much throughput you are getting. you will get 100% result.
    • Sumit Sharma Sarvesh Dubey .. Good to c u .. !!
      7 hrs · Like · 1
    • Sumit Sharma Little Probing I will do. ( 1) first confirm if at PE end, capping is actually done for 144. ( 2 ) If things are OK at ISP, we need to verify from our end if we are getting the committed speed, for testing I recommend do not check live traffic or some download which will obviously do not show the actual bandwidth. Go for some third party software which pushes traffic to the maximum limit on the link, which is equal to bandwidth of link.

                              49 mins · Like · Remove Preview

                               Sumit Sharma
                               Write a comment…

 

FB DISCUSSIONS: BGP RIB FAILURE


INFOSYS INTERVIEW
In BGP routes, if routes are learned with symbol ‘r’.
What is the meaning of symbol ‘r’?
Explain some scenario for illustration ?

Like · ·

 

FB DISCUSSIONS: WHY WE NEED IP ADDRESS ?


CISCO INTERVIEW
We have the MAC address to uniquely identify the network components ?
Then, why we need the IP address for identification ?
What is the logic ?
Complete Set Of Questions, click below
https://networkproxy.wordpress.com/…/company-interview-ques…/

Like · ·
  • Chakkaravarthi Vinayagam In layered architecture we can’t route the packets with the help of #MAC_address if we do so our entire internet domain act as a single cluster. If we use #IP_address we can create multiple cluster like what we have in today internet domain. We can able to identify problems and avoid unnecessary routing into our private network.
  • Sajad Wani Bcoz , mac communication is limited to layer 2 of the device , for global identification we need ip address which works on layer 3 of the device
  • Rytesh Vishwakarma ip is used to locate the network
    Mac is used to locate the host on that network.
    While communicating with remote hosts we dont use the mac of the destination host instead we use the mac of our default gateway….
    Our ip takes us to that network afterwards we use arp to find the mac of the destination host.
    • Cisco Sahil Thats right .. Both are used for identification …. But there should be some logic behind using each & every term. Will check out ..
    • Ajay Kumar interfaces can be change while ip network ID remain same
    • Ajay Kumar when we trace someone……….. you can understand what we do or what we can
    • Cisco Sahil Here, we are talking about mechanism, which is perfectly right, as said in above comments. But friends we need some more strong logic to justify.
    • Rytesh Vishwakarma ip is used to locate the network Mac is used to locate the host on that network. While communicating with remote hosts we dont use the mac of the destination host instead we use the mac of our default gateway…. Our ip takes us to that network afterwards we use arp to find the mac of the destination host.
    • Aditya Uppalapati In case of multi layer switch we can use two commands to locate the switch port and router port
    • Cisco Sahil Ajay Kumar .. Yes you are right, using Layer 2 trace route & Layer 3 trace route, we can understand complete network. This is the mechanism to understand. But we need to go into background to understand the designing basics of MAC address & IP.
    • Usman Tahir we need the ip address to logically identify the hosts because the ip address is logical address to send traffic between the end to end hosts.
    • Usman Tahir in other words mac address is used to identify a host only on a link but ip address is used to identify a host within the whole network.
      • Bhasker Reddy Each sub interface can assign logical ip but we cant assign 1 mac address to ever sub interfaces
      • Sajad Wani Ya Rytesh ! Frame never leaves the default gateway , now the frame will be encapsulated(packet) with the Ip address and decapsulated on the other end.
      • Mohammed Yunus mac address is identification , and Ip is an address , for ex : post letter Name is identification (mac) and Address is IP , without name or address we cont send the letter , that’s like mac and Ip
      • Mohammed Yunus mac address is identification , and Ip is an address , for ex : post letter Name is identification (mac) and Address is IP , without name or address we cont send the letter , that’s like mac and Ip
      • Adel Issad We have the MAC @ to identify the network components but IP @ identify where is the component is in the network (identify the component end the subnet)
      • Sumit Sharma Complete set of questions given on below link
      • Sumit Sharma https://networkproxy.wordpress.com/…/company-interview…/

        BASED ON CANDIDATE’S EXPERIENCE’S DATE:…
        NETWORKPROXY.WORDPRESS.COM
        • Sumit Sharma UPDATED: 18-12-14
        • Sumit Sharma Dear Members, Thanks all for your inputs. Everyone got the right point. Mechanism explanation is absolutely right.
        • Fahad Ahmed If a device or a host is on another network, then we need to have its ip address as the routers need ip address of a machine to forward the packets.
        • Sumit Sharma One very good logic given by candidate: MAC address is used for identification, true, But MAC addresses cannot be summarized, Individually they could have made the routing table very large, which is impossible to be handled by the network devices. Whereas, IP’s can be summarized, this is what we are doing in our network, that’s why network devices are able to handle routing tables.
        • Jameel we need ip addresses to route traffic
        • Manish Sharma Hi….the reason could be for mac- address there is no hierarchy…..so it would be difficult to separate one network from another….but for IP addressing we can logically divide this and thus it is used …
        • Noor Mohamad Kanjwal mac address r like finger print… its uniq 4 every human but we use names to identfy them ..same way we use ip address to identfy ny device..its logical address easy to use n remember than mac address
          • Mohamed Salman this was my ques when i just started ccna and i ended up makin my own ans just as Sumit Sharma mentioned…but my way of thinkin ws ip address is kinda standard and everyone uses the same standard whc ends up doin SUMMERIZATION ..but when it comes in terms of MAC the 1st part is vender specific..if som new vender comes up tomm then he will make up his own range of MAC which would mess up things if we are communicating in wan in terms of MAC.. i hope i was able to keep my thought
          • Fahad Ahmed Sumit Mac address is used to identify a device or a host on LAN but IP address is used to identify a device or a host on Internet.
          • Asan Mydeen E S IP addresses (Network portion) are used to locate the networks whereas the Mac address are used to find the host within the Lan network (by ARP )
          • Priyanka Nath MAC address for Switched network.
            IP address for Rouing network.
          • Sumit Sharma Mohamed Salman .. You got the right logic .. !!
          • Sumit Sharma One thing: SCALABILITY: IP’s have standard format, MAC address don’t have ( Varies from vendor to vendor ). So, there cannot be summarization. Without summarization, Its not feasible at all to handle routing table in live environment. This is a strong reason, we are using ip’s.
            20 hrs · Like · 4
          • Fahad Ahmed But don’t mac address has 13 bits notation?
          • Abhay Karanwal a network consist of Ethernet cable, serial cable, FR PVCs and ATM PVCs, MPLS …… all the medium have different header type at layer two.