External veth of every Rattan instance has the same MAC and IP addresses

[Centaurus99]

rattan/rattan-core/src/env.rs

Lines 295 to 325 in acd3e01

	// Build veth0 for left and right, which are reserved for external connection, but ignore it for now
	let left_veth0 = VethPairBuilder::new()
	.name(
	format!("vL0-L-{rand_string}"),
	format!("vL0-R-{rand_string}"),
	)
	.namespace(Some(left_netns.clone()), Some(rattan_netns.clone()))
	.mac_addr(
	[0x38, 0x7e, 0x58, 0xe7, 1, 1].into(),
	[0x38, 0x7e, 0x58, 0xe7, 1, 2].into(),
	)
	.ip_addr(
	(IpAddr::V4(Ipv4Addr::new(192, 168, 1, 1)), 32),
	(IpAddr::V4(Ipv4Addr::new(192, 168, 1, 2)), 32),
	)
	.build()?;
	let right_veth0 = VethPairBuilder::new()
	.name(
	format!("vR0-L-{rand_string}"),
	format!("vR0-R-{rand_string}"),
	)
	.namespace(Some(rattan_netns.clone()), Some(right_netns.clone()))
	.mac_addr(
	[0x38, 0x7e, 0x58, 0xe7, 2, 2].into(),
	[0x38, 0x7e, 0x58, 0xe7, 2, 1].into(),
	)
	.ip_addr(
	(IpAddr::V4(Ipv4Addr::new(192, 168, 2, 2)), 32),
	(IpAddr::V4(Ipv4Addr::new(192, 168, 2, 1)), 32),
	)
	.build()?;

Although the external veth currently serves no practical purpose, this behavior might lead to user confusion and complicate network configuration at runtime.

Suggestions:

1. Similar to how other veths are constructed, generate unique MAC and IP addresses for the external veth of each instance.
2. By default, do not create the external veth.