Eternal doesn't always mean eternal...., if it did there would be contradictions in the bible. Sodom didn't burn for eternity it's consequences are eternal. We should understand this when we read verses referring to the eternal hell. The fire of hell will be eternal not burning for eternity but the result will be for ever and ever.
Luk_17:29 But the same day that Lot went out of Sodom it rained fire and brimstone from heaven, and destroyed them all.
Jud_1:7 Even as Sodom and Gomorrha, and the cities about them in like manner, giving themselves over to fornication, and going after strange flesh, are set forth for an example, suffering the vengeance of eternal fire.
It is my understanding from my Hebrew NT is the they are experiencing the eternal fire now and more after the judgement.
Robertson Word Pictures:
Suffering (
upexousai). Present active participle of
upexw, old compound, to hold under, often with
dikhn (right, justice, sentence II Thessalonians 1:9) to suffer sentence (punishment), here only in N.T.
Of eternal fire (
purov aiwniou). Like
desmoiv aidioiv in verse
Judges 1:7. Cf. the
hell of fire (
Matthew 5:22) and also
Matthew 25:46. Jude has no mention of Lot.
Jude 7
Expanded Bible
7 Also remember the cities of Sodom and Gomorrah [C destroyed by God for their evil;
Gen. 19;
2 Pet. 2:6] and the other towns around them. In the same way they were full of sexual sin and people who ·desired sexual relations that God does not allow [pursued sexual perversion; L departed after different flesh].
They suffer the punishment of eternal fire, as an ·example [warning] for all to see.
They suffer the punishment of eternal fire, is present tense.
Jude
5 I want to help you remember some things you already know: Remember that the Lord[
a] saved his people by bringing them out of the land of Egypt. But later he destroyed all those who did not believe. 6 And remember the angels who lost their authority to rule. They left their proper home. So
the Lord has kept them in darkness, bound with everlasting chains, to be judged on the great day. 7 Also, remember the cities of Sodom and Gomorrah and the other towns around them. Like those angels they were full of sexual sin and involved themselves in sexual relations that are wrong. And
they suffer the punishment of eternal fire, an example for us to see.
Both the angels being held and suffering the punishment are present tense.
Are you aware of any passages in the OT that says God used eternal fire to destroy Sodom?
Gen 19
24 and the Lord began to destroy Sodom and Gomorrah. He caused fire and burning sulfur to fall from the sky. 25 He destroyed the whole valley—all the cities, the people living in the cities, and all the plants in the valley.
As you can see Genesis does NOT say it was eternal fire.