Cisco Switching And Routing Pdf

[Shantelle Wenske]

Ihave a customer that is doing a migration. And when we change the default gateway, it causes problem. However, based on my understanding of how L2 and L3 switching and routing works, it should not. I would just like some clarification to my understanding.

When a client makes a connection, it ARPs and receives the address on the old internet router (im skipping multiple hops, but lets assume we are directly connected). The frame is then sent from the client with the original source IP/MAC, and the destination public IP of the PPTP server and Router MAC. The router forwards the frame with the original client IP and Router MAC, destined to the server Internal IP (NAT occurs here) and server MAC. On the return path, the server send the reply to the IP and mac it received (the client IP, and MAC of router) and its own internal IP/MAC. the router receives this, reverse NATs the server Internal IP to the Public IP, replaces the server source MAC with the router MAC, and swaps the destination MAC with the client MAC, and sends back to the client IP and client original MAC. At this point, the PPTP should setup...

The server will never initiate the converstion, so it should never have to ARP the new gateway for the public IP, thus getting the new gateway and using that path. It should only need to respond to requests using the destination MAC of the router...

If thats the case and you need to keep the default route on the core switch pointing at your new router then you could configure a policy route for the traffic that is from the IP address of the PPTP Server on the core switch, maybe.

The PPTP connection actually is established to an external IP, NAT's to an internal IP of the PPTP server (10.33.20.?). So yes it comes through the old router (Internal interface- 10.33.20.1), to an inside PPTP server. All default gateways internally point to a new core switch (10.33.20.2), which then points to the new gateway (10.33.20.250). I also missed a detail, the new router isnt a router, its a firewall. But the topology remains the same

Everything connects to the core switch. The diagram would be the cors switch in the center, with all nodes connected to it, i am sorry i dont have an image to upload at the moment, but here is a rough attempts.

The PPTP is responding to the request, shouldnt it use the MAC of the router that the request came in on, and then respond using that as the destination? When the request came in, it came in with source IP if client, and source of router, shouldnt it have stored that binding and responded used that? I am just not sure why the PPTP server's gateway would ever come into play.

Routers operate at layer 3 and therefore do not forward ARP (layer 2) requests. If a host wanted to communicate with another host on a different segment then it will ARP for the MAC address of its default gateway.

My question was, if a remote node on another subnet came in on another router, why wouldn't it use that routers mac instead of the default gateway, and the only answer i can come up with is that the device maps the mac of its default gateway and uses that ONLY anytime a remote request comes in. So even if communication is established through another router, the device sees a remote IP and says "OH, send all remote IPs to this MAC (of the default gateway) regardless of where it came from...(Not actually caring or paying attention to what MAC it came from)"

The host will simply compare the destination IP address to its local subnet. If the IP address is different to its local subnet it knows to send it to its default gateway. If it doesn't have an ARP entry for its local gateway it will ARP for that IP and NOT the destination IP.

In this sample chapter from Switching, Routing, and Wireless Essentials Companion Guide (CCNAv7) for Cisco Networking Academy students, you will learn how to troubleshoot common inter-VLAN configuration issues.

Modern enterprise networks rarely use router-on-a-stick because it does not scale easily to meet requirements. In these very large networks, network administrators use Layer 3 switches to configure inter-VLAN routing.

Inter-VLAN routing using the router-on-a-stick method is simple to implement for a small- to medium-sized organization. However, a large enterprise requires a faster, much more scalable method to provide inter-VLAN routing.

Enterprise campus LANs use Layer 3 switches to provide inter-VLAN routing. Layer 3 switches use hardware-based switching to achieve higher-packet processing rates than routers. Layer 3 switches are also commonly implemented in enterprise distribution layer wiring closets.

To provide inter-VLAN routing, Layer 3 switches use SVIs. SVIs are configured using the same interface vlan vlan-id command used to create the management SVI on a Layer 2 switch. A Layer 3 SVI must be created for each of the routable VLANs.

In Figure 4-6, the Layer 3 switch, D1, is connected to two hosts on different VLANs. PC1 is in VLAN 10, and PC2 is in VLAN 20, as shown. The Layer 3 switch will provide inter-VLAN routing services to the two hosts.

Step 2. Create the SVI VLAN interfaces. Configure the SVI for VLANs 10 and 20, as shown in Example 4-14. The IP addresses that are configured will serve as the default gateways to the hosts in the respective VLANs. Notice the informational messages showing the line protocol on both SVIs changed to up.

Step 4. Enable IP routing. Finally, enable IPv4 routing with the ip routing global configuration command to allow traffic to be exchanged between VLANs 10 and 20, as shown in Example 4-16. This command must be configured to enable inter-VAN routing on a Layer 3 switch for IPv4.

Inter-VLAN routing using a Layer 3 switch is simpler to configure than the router-on-a-stick method. After the configuration is complete, the configuration can be verified by testing connectivity between the hosts.

From a host, verify connectivity to a host in another VLAN using the ping command. It is a good idea to first verify the current host IP configuration using the ipconfig Windows host command. The output in Example 4-17 confirms the IPv4 address and default gateway of PC1.

Next, verify connectivity with PC2 using the ping Windows host command, as shown in Example 4-18. The ping output successfully confirms that inter-VLAN routing is operating.

A routed port is created on a Layer 3 switch by disabling the switchport feature on a Layer 2 port that is connected to another Layer 3 device. Specifically, configuring the no switchport interface configuration command on a Layer 2 port converts it into a Layer 3 interface. Then the interface can be configured with an IPv4 configuration to connect to a router or another Layer 3 switch.

OSPF routing configuration is covered in another course. In this module, OSPF configuration commands will be given to you in all activities and assessments. It is not required that you understand the configuration in order to enable OSPF routing on the Layer 3 switch.

Step 3. Configure routing. Configure the OSPF routing protocol to advertise the VLAN 10 and VLAN 20 networks, along with the network that is connected to R1, as shown in Example 4-21. Notice the message informing you that an adjacency has been established with R1.

Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Cisco Press products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

3a8082e126