pace-it: common wan components and issues

Common WAN components and issues.

Instructor, PACE-IT Program – Edmonds Community College

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M.B.A., IT Management, Western Governor’s University

B.S., IT Security, Western Governor’s University

Entrepreneur, executive leader, and proven manger with 10+ years of experience turning complex issues into efficient and effective solutions.

Strengths include developing and mentoring diverse workforces, improving processes, analyzing business needs and creating the solutions required— with a focus on technology.

Brian K. Ferrill, M.B.A.


– Common WAN components.

– Common WAN issues.

PACE-IT.

Common WAN components.Common WAN components and issues.

Common WAN components.

– Copper line drivers or repeaters.» These are used to allow network traffic to go farther

distances over copper wire type networks (e.g., the PSTN network).

• They take an incoming signal and regenerate it (boosting the strength) and then send it back out, thus reducing attenuation.

– Demarc.» Demarc = the demarcation point: the physical point

where the telecommunication company’s (Telco's) responsibility ends and the customer’s begins.

• The Telco takes care of the upstream end of the network.

» The demarc may be simple or very complex, depending on the size of the organization and the required services.

– Network interface unit (NIU).» In the SOHO environment, the NIU is usually the

demarc.» In the SOHO environment, the NIU is usually provided

by the Internet service provider (ISP).• An NIU can be a cable modem, a DSL modem, or

another piece of hardware that connects the customer to the ISP.



– SmartJack.» An NIU that can provide feedback on conditions to the

ISP.• SmartJacks can help the ISP determine if a problem

exists on its end of the demarc through the use of remote loopback capabilities.

• Many SmartJacks can provide translation between protocols (e.g., translating a serial PPP communication stream into Ethernet).

– Channel Service Unit/Digital Service Unit (CSU/DSU).

» The interface that provides the connection between a point-to-point line (T1) and the device that is directing network traffic, usually a router.

• The CSU/DSU may be an external device, or it may be a removable module inside a router.

• Only two CSU/DSUs may exist on a single point-to-point line—one at either end of the connection.


Common WAN issues.Common WAN components and issues.

Common WAN issues.

– Loss of Internet connectivity issues.» Many factors can lead to a loss of connectivity—on

both sides of the demarc.• Before contacting the WAN provider, check the local

area network (LAN) equipment for its operation. If the issue is not found to be on the LAN side, contact the WAN provider.

• One of the tests that the WAN provider will conduct is a loopback test to check its line for interference.

– DNS issues.» May look like a loss of Internet connectivity, but it isn’t

(e.g., users cannot connect to www.google.com).» If using a local DNS server, verify the settings and

make corrections accordingly.» If using the WAN provider’s DNS settings, attempt to

ping the IP address; if that works, there is a WAN connection.

• If you use the ping utility with the fully qualified domain name and this fails, contact the WAN provider to resolve this issue.


Common WAN issues.

– Interface issues.» Errors on a router’s WAN interface can indicate several

different issues. Monitoring an interface’s status and reading the error reports may provide a clue as to the issue.

» The most common issue that prevents a good connection is a speed or duplex mismatch.

• A speed mismatch between the interfaces will prevent a link from being established.

• A duplex mismatch between the interface will create errors (e.g., output and input errors).

» Discards and packet drops:• If the device is discarding incoming packets, then,

more than likely, the device’s CPU is being overutilized.

• If the device is dropping outgoing packets, then there is a bandwidth congestion issue (which may be caused by interference on the line).


Common WAN issues.

– Router configuration issues.» A common problem when establishing a new WAN

connection.• A misconfiguration of the WAN interface of a router

will lead to a WAN connection issue.• If this is suspected, verify the proper configuration

settings with the WAN provider.

– Company policy and practice issues.» Unfortunately, there are some company policies and

practices that may appear to end users as WAN connection issues.

• Some applications may be throttled (have their available bandwidth reduced for quality of service (QoS) reasons), leading to slow services (a perceived WAN issue).

• Acceptable use policies may restrict or block access to certain sites or types of sites, which may appear to the end user as a WAN issue.


Common WAN issues.

– Satellite issues.» If a satellite WAN connection is used, latency will

increase due to the distances covered.• Latency is the measure of time between the sending

of data and the receiving of data.• Careful application of QoS techniques may mitigate

the effects of latency on some applications.

– Split horizon issues.» A technique used in routing to help prevent routing

loops.• With split horizon, a router will not advertise a route to

another network out of the interface it learned the route on.

» With a point-to-multipoint WAN connection, the router may have difficulty with split horizon.

• It will learn all of the routes on the same interface, but can’t advertise those routes back out of the interface.

» Creating logical sub-interfaces on the WAN interface will usually resolve this issue.

• The logical sub-interfaces appear to the router as individual interfaces, allowing the router to advertise the routes back out of the WAN interface.


What was covered.Common WAN components and issues.

There are several important components that help to make up a WAN connection. Some of them are the WAN provider’s responsibility, including the copper line drivers or repeaters and the NIU or SmartJack. A shared responsibility would include the demarc, while the client’s responsibility includes the CSU/DSU.

Topic


Summary

Common WAN issues include: loss of Internet connectivity, DNS issues, interface issues, router configuration issues, perceived issues due to company policies and practices, satellite issues, and split horizon issues.

Common WAN issues.

THANK YOU!

This workforce solution was 100 percent funded by a $3 million grant awarded by the U.S. Department of Labor's Employment and Training Administration. The solution was created by the grantee and does not necessarily reflect the official position of the U.S. Department of Labor. The Department of Labor makes no guarantees, warranties, or assurances of any kind, express or implied, with respect to such information, including any information on linked sites and including, but not limited to, accuracy of the information or its completeness, timeliness, usefulness, adequacy, continued availability or ownership. Funded by the Department of Labor, Employment and Training Administration, Grant #TC-23745-12-60-A-53.

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pace-it: common wan components and issues

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