RE: Ethernet switching
a station doesn't send an ARP for a station not on its subnet. (There are workarounds to this, such as not configuring a default gateway I don't believe that this is correct. If there is no route, default or better, to the other (sub)network, then you'll get something like "network unreachable" or "host unreachable" or making the default gateway your own address.) This is the trick that I was talking about -- more specifically, adding a route to the *particular* (sub)network of the other node, rather than the disruptive default route. ... and I've actually used it, but, I never thought too deeply about how it works. I (the PC with default-to-self) still have to get the packet to the other node, whose destination IP address is on another IP subnet (even though we're "on the same wire"). So, ISTM, I have 2 choices: 1: put the packet out as a local MAC broadcast or 2. Do an ARP for the other IP address, even though it's not in my logical IP (sub)network. (I'm certainly *not* going to ARP for own address (which is now the default gateway). ) Either choice is non-normal (or, at least, non-familiar :) behavior, so I'm wondering whether this is defined somewhere in an RFC? Actually, is this trick discussed *anywhere* ? OTOH, maybe I'm just being dense and it's not a "trick" at all, but dunangme if I can figger out how it works :| --- Tks | [EMAIL PROTECTED] BV | [EMAIL PROTECTED] Sr. Tech. Consultant,SBM Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 === -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Priscilla Oppenheimer Sent: Wednesday, January 31, 2001 8:48 PM To: [EMAIL PROTECTED] Subject: RE: Ethernet switching At 04:32 PM 1/31/01, Fred Danson wrote: Ok, now from my understanding, each port on a switch is its own collision domain. As far as broadcast domains go, if a switch is not setup for multiple VLANs, then everything on the switch is considered to be in the same broadcast domain, no matter what is running at layer 3. You are right. The original reply that brought collision domains into the picture muddied the waters. You make an important point about broadcasting. I think people forget that all devices on a switched network (regardless of IP subnetting or other layer-3 issues) hear each other's broadcasts, unless VLANs are configured. The other thing that was missing, though, (as many people have mentioned), was that a station doesn't send an ARP for a station not on its subnet. (There are workarounds to this, such as not configuring a default gateway or making the default gateway your own address.) Priscilla _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Ethernet switching
Depends on the subnet mask you are using, for instance 142.102.3.1 with a subnet mask of 255.255.0.0 142.102.2.1 also with a subnet of 255.255.0.0 The 2.1 and 3.1 would be on the same subnet, however if you have a different subnet mask I don't think it would work. Joey -Original Message- From: alexs [mailto:[EMAIL PROTECTED]] Sent: Saturday, September 09, 2000 7:42 AM To: [EMAIL PROTECTED] Subject: Ethernet switching Hello everyone, I have a question that probably will sound silly but here it is: Suppose that you take a new 2924 out of the box and you plug in two PC's. You assign address, for example, 142.102.2.1 to the first one and 142.102.3.1 to the second one.There is not any router in this small network.142.102.2.1 tries to ping 142.102.3.1.The question is: will 142.102.2.1 get a reply and why? Thanks alexs _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Ethernet switching
These are my thoughts, If the switch was right out of the box, the stations could ping each other no matter what subnet mask you were using. The reason being, they are located in the same broadcast domain, vlan1. This is the default vlan for all switched ports at this time. The first station would arp for the other, it would get a response because they are on the same layer 2 broadcast domain and they could speak directly using the switch. Switches by default with no mls, are layer two devices. They have no concept of IP. They make decision based on layer 2 MAC addresses and the ports they are connected to. If these stations were in different vlans, the situation would change. You then have created two broadcast domains and in order for the devices to talk, a router or mls entry would be needed. Someone please correct me if I am wrong. -Original Message- From: Fowler, Joey To: [EMAIL PROTECTED] Sent: 1/31/01 10:52 AM Subject: RE: Ethernet switching Depends on the subnet mask you are using, for instance 142.102.3.1 with a subnet mask of 255.255.0.0 142.102.2.1 also with a subnet of 255.255.0.0 The 2.1 and 3.1 would be on the same subnet, however if you have a different subnet mask I don't think it would work. Joey -Original Message- From: alexs [mailto:[EMAIL PROTECTED]] Sent: Saturday, September 09, 2000 7:42 AM To: [EMAIL PROTECTED] Subject: Ethernet switching Hello everyone, I have a question that probably will sound silly but here it is: Suppose that you take a new 2924 out of the box and you plug in two PC's. You assign address, for example, 142.102.2.1 to the first one and 142.102.3.1 to the second one.There is not any router in this small network.142.102.2.1 tries to ping 142.102.3.1.The question is: will 142.102.2.1 get a reply and why? Thanks alexs _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Ethernet switching
I don't believe that this is correct. Let's say that you had one set to 10.1.1.1/24, and the other to 172.16.1.1/24. If you are at 10.1.1.1 and try to ping 172.16.1.1, your station will compare the destination address to your own IP/mask combination and discover that the destination is not local. It will not arp for the destination MAC address, but will forward the packet to the default gateway. An arp would only be transmitted if your station determined that the destination was local and there was no corresponding entry in the arp cache. It's true these devices are in the same broadcast domain, meaning that station 2 would see arp requests from station 1, but in this given scenario no arp request would occur. In this scenario , it would also not matter what ip address you assigned to the stations . ie: you could set one at 10.x.x.x /8 and the other at 192.x.x.x/28 and still get a ping response Kane - Original Message - From: "Sheahan, Ryan" [EMAIL PROTECTED] To: "'Fowler, Joey '" [EMAIL PROTECTED]; [EMAIL PROTECTED] Sent: Thursday, February 01, 2001 5:23 AM Subject: RE: Ethernet switching These are my thoughts, If the switch was right out of the box, the stations could ping each other no matter what subnet mask you were using. The reason being, they are located in the same broadcast domain, vlan1. This is the default vlan for all switched ports at this time. The first station would arp for the other, it would get a response because they are on the same layer 2 broadcast domain and they could speak directly using the switch. Switches by default with no mls, are layer two devices. They have no concept of IP. They make decision based on layer 2 MAC addresses and the ports they are connected to. If these stations were in different vlans, the situation would change. You then have created two broadcast domains and in order for the devices to talk, a router or mls entry would be needed. Someone please correct me if I am wrong. -Original Message- From: Fowler, Joey To: [EMAIL PROTECTED] Sent: 1/31/01 10:52 AM Subject: RE: Ethernet switching Depends on the subnet mask you are using, for instance 142.102.3.1 with a subnet mask of 255.255.0.0 142.102.2.1 also with a subnet of 255.255.0.0 The 2.1 and 3.1 would be on the same subnet, however if you have a different subnet mask I don't think it would work. Joey -Original Message- From: alexs [mailto:[EMAIL PROTECTED]] Sent: Saturday, September 09, 2000 7:42 AM To: [EMAIL PROTECTED] Subject: Ethernet switching Hello everyone, I have a question that probably will sound silly but here it is: Suppose that you take a new 2924 out of the box and you plug in two PC's. You assign address, for example, 142.102.2.1 to the first one and 142.102.3.1 to the second one.There is not any router in this small network.142.102.2.1 tries to ping 142.102.3.1.The question is: will 142.102.2.1 get a reply and why? Thanks alexs _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] ___ Send a cool gift with your E-Card http://www.bluemountain.com/giftcenter/ _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Ethernet switching
Duh , scrub that it doesn't work , it works really well when your stations are dual homed though ; ) Kane - Original Message - From: "Kane" [EMAIL PROTECTED] To: "Sheahan, Ryan" [EMAIL PROTECTED]; "'Fowler, Joey '" [EMAIL PROTECTED]; [EMAIL PROTECTED] Sent: Thursday, February 01, 2001 9:08 AM Subject: Re: Ethernet switching In this scenario , it would also not matter what ip address you assigned to the stations . ie: you could set one at 10.x.x.x /8 and the other at 192.x.x.x/28 and still get a ping response Kane - Original Message - From: "Sheahan, Ryan" [EMAIL PROTECTED] To: "'Fowler, Joey '" [EMAIL PROTECTED]; [EMAIL PROTECTED] Sent: Thursday, February 01, 2001 5:23 AM Subject: RE: Ethernet switching These are my thoughts, If the switch was right out of the box, the stations could ping each other no matter what subnet mask you were using. The reason being, they are located in the same broadcast domain, vlan1. This is the default vlan for all switched ports at this time. The first station would arp for the other, it would get a response because they are on the same layer 2 broadcast domain and they could speak directly using the switch. Switches by default with no mls, are layer two devices. They have no concept of IP. They make decision based on layer 2 MAC addresses and the ports they are connected to. If these stations were in different vlans, the situation would change. You then have created two broadcast domains and in order for the devices to talk, a router or mls entry would be needed. Someone please correct me if I am wrong. -Original Message- From: Fowler, Joey To: [EMAIL PROTECTED] Sent: 1/31/01 10:52 AM Subject: RE: Ethernet switching Depends on the subnet mask you are using, for instance 142.102.3.1 with a subnet mask of 255.255.0.0 142.102.2.1 also with a subnet of 255.255.0.0 The 2.1 and 3.1 would be on the same subnet, however if you have a different subnet mask I don't think it would work. Joey -Original Message- From: alexs [mailto:[EMAIL PROTECTED]] Sent: Saturday, September 09, 2000 7:42 AM To: [EMAIL PROTECTED] Subject: Ethernet switching Hello everyone, I have a question that probably will sound silly but here it is: Suppose that you take a new 2924 out of the box and you plug in two PC's. You assign address, for example, 142.102.2.1 to the first one and 142.102.3.1 to the second one.There is not any router in this small network.142.102.2.1 tries to ping 142.102.3.1.The question is: will 142.102.2.1 get a reply and why? Thanks alexs _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Ethernet switching
In this scenario , it would also not matter what ip address you assigned to the stations . ie: you could set one at 10.x.x.x /8 and the other at 192.x.x.x/28 and still get a ping response Kane It was my understanding that IP will compare the source subnet mask to the source IP address, and if the destination IP address/subnet mask combo doesn't put it on the same network as the source, the packet will automatically be forwarded to the default gateway. A router would then have to forward the packet to the right interface, even if it is on the same interface. So if there were 2 networks like that in the same broadcast domain, they would have to go through a router to talk to eachother. Someone please correct me if I'm wrong. Thanks, Freddy Flinstone From: "Kane" [EMAIL PROTECTED] Reply-To: "Kane" [EMAIL PROTECTED] To: "Sheahan, Ryan" [EMAIL PROTECTED],"'Fowler, Joey '" [EMAIL PROTECTED], [EMAIL PROTECTED] Subject: Re: Ethernet switching Date: Thu, 1 Feb 2001 09:08:09 +1300 - Original Message - From: "Sheahan, Ryan" [EMAIL PROTECTED] To: "'Fowler, Joey '" [EMAIL PROTECTED]; [EMAIL PROTECTED] Sent: Thursday, February 01, 2001 5:23 AM Subject: RE: Ethernet switching These are my thoughts, If the switch was right out of the box, the stations could ping each other no matter what subnet mask you were using. The reason being, they are located in the same broadcast domain, vlan1. This is the default vlan for all switched ports at this time. The first station would arp for the other, it would get a response because they are on the same layer 2 broadcast domain and they could speak directly using the switch. Switches by default with no mls, are layer two devices. They have no concept of IP. They make decision based on layer 2 MAC addresses and the ports they are connected to. If these stations were in different vlans, the situation would change. You then have created two broadcast domains and in order for the devices to talk, a router or mls entry would be needed. Someone please correct me if I am wrong. -Original Message- From: Fowler, Joey To: [EMAIL PROTECTED] Sent: 1/31/01 10:52 AM Subject: RE: Ethernet switching Depends on the subnet mask you are using, for instance 142.102.3.1 with a subnet mask of 255.255.0.0 142.102.2.1 also with a subnet of 255.255.0.0 The 2.1 and 3.1 would be on the same subnet, however if you have a different subnet mask I don't think it would work. Joey -Original Message- From: alexs [mailto:[EMAIL PROTECTED]] Sent: Saturday, September 09, 2000 7:42 AM To: [EMAIL PROTECTED] Subject: Ethernet switching Hello everyone, I have a question that probably will sound silly but here it is: Suppose that you take a new 2924 out of the box and you plug in two PC's. You assign address, for example, 142.102.2.1 to the first one and 142.102.3.1 to the second one.There is not any router in this small network.142.102.2.1 tries to ping 142.102.3.1.The question is: will 142.102.2.1 get a reply and why? Thanks alexs _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ Get your FREE download of MSN Explorer at http://explorer.msn.com _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Ethernet switching
Before an ARP is done, however, the PC would see if the other host is on the same subnet. If not, it would look for a route to the other's network. In the case of /24 mask, they are on different subnets, so no ARP would be done. However, IIRC, there is a trick that can work, at least on PCs -- if both PCs have their default route set to their own interface IP address, then the ARP *is* done and they can talk. Someone else'll remember the details better than I. - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Sheahan, Ryan Sent: Wednesday, January 31, 2001 11:24 AM To: 'Fowler, Joey '; '[EMAIL PROTECTED] ' Subject: RE: Ethernet switching These are my thoughts, If the switch was right out of the box, the stations could ping each other no matter what subnet mask you were using. The reason being, they are located in the same broadcast domain, vlan1. This is the default vlan for all switched ports at this time. The first station would arp for the other, it would get a response because they are on the same layer 2 broadcast domain and they could speak directly using the switch. Switches by default with no mls, are layer two devices. They have no concept of IP. They make decision based on layer 2 MAC addresses and the ports they are connected to. If these stations were in different vlans, the situation would change. You then have created two broadcast domains and in order for the devices to talk, a router or mls entry would be needed. Someone please correct me if I am wrong. -Original Message- From: Fowler, Joey To: [EMAIL PROTECTED] Sent: 1/31/01 10:52 AM Subject: RE: Ethernet switching Depends on the subnet mask you are using, for instance 142.102.3.1 with a subnet mask of 255.255.0.0 142.102.2.1 also with a subnet of 255.255.0.0 The 2.1 and 3.1 would be on the same subnet, however if you have a different subnet mask I don't think it would work. Joey -Original Message- From: alexs [mailto:[EMAIL PROTECTED]] Sent: Saturday, September 09, 2000 7:42 AM To: [EMAIL PROTECTED] Subject: Ethernet switching Hello everyone, I have a question that probably will sound silly but here it is: Suppose that you take a new 2924 out of the box and you plug in two PC's. You assign address, for example, 142.102.2.1 to the first one and 142.102.3.1 to the second one.There is not any router in this small network.142.102.2.1 tries to ping 142.102.3.1.The question is: will 142.102.2.1 get a reply and why? Thanks alexs _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Ethernet switching
At 11:23 AM 1/31/01, Sheahan, Ryan wrote: These are my thoughts, If the switch was right out of the box, the stations could ping each other no matter what subnet mask you were using. The reason being, they are located in the same broadcast domain, vlan1. This is the default vlan for all switched ports at this time. The first station would arp for the other, it would get a response because they are on the same layer 2 broadcast domain and they could speak directly using the switch. If the subnet mask indicated the stations were not on the same subnet, the station would not ARP for the other station. It would ARP for the default gateway. So it wouldn't work "out of the box." Priscilla Switches by default with no mls, are layer two devices. They have no concept of IP. They make decision based on layer 2 MAC addresses and the ports they are connected to. If these stations were in different vlans, the situation would change. You then have created two broadcast domains and in order for the devices to talk, a router or mls entry would be needed. Someone please correct me if I am wrong. -Original Message- From: Fowler, Joey To: [EMAIL PROTECTED] Sent: 1/31/01 10:52 AM Subject: RE: Ethernet switching Depends on the subnet mask you are using, for instance 142.102.3.1 with a subnet mask of 255.255.0.0 142.102.2.1 also with a subnet of 255.255.0.0 The 2.1 and 3.1 would be on the same subnet, however if you have a different subnet mask I don't think it would work. Joey -Original Message- From: alexs [mailto:[EMAIL PROTECTED]] Sent: Saturday, September 09, 2000 7:42 AM To: [EMAIL PROTECTED] Subject: Ethernet switching Hello everyone, I have a question that probably will sound silly but here it is: Suppose that you take a new 2924 out of the box and you plug in two PC's. You assign address, for example, 142.102.2.1 to the first one and 142.102.3.1 to the second one.There is not any router in this small network.142.102.2.1 tries to ping 142.102.3.1.The question is: will 142.102.2.1 get a reply and why? Thanks alexs _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Priscilla Oppenheimer http://www.priscilla.com _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
